Abstract: A closed loop drilling fluids circulation system includes a first drilling fluid circulation system disposed at a first subterranean drill site. The first drilling fluid circulation system includes a supply tank for holding clean drilling fluid and a solids control device configured to separate solids from used drilling fluid. In addition, the system includes a central processing facility disposed at a location remote from the first drill site and configured to receive used drilling fluid from the solids control device and supply clean drilling fluid to the supply tank.

Abstract: As system for measuring drilling fluid properties includes a capillary rheometer that is adapted to measure viscosity parameters of drilling fluid. The capillary rheometer includes a feed chamber, the feed chamber having a cavity, at least a first drain port for draining fluid out of the cavity, a double wall defining an annulus that opens to the cavity, and a feed port in an outer portion of the double wall that is in fluid communication with the annulus. The capillary rheometer also includes at least a first capillary tube coupled to at least the first drain port. Additionally, the disclosed system further includes a pump that is adapted to pump fluid to the feed port.

Abstract: A method of controlling standpipe pressure in a drilling operation can include comparing a measured standpipe pressure to a desired standpipe pressure, and automatically adjusting a choke in response to the comparing, thereby reducing a difference between the measured standpipe pressure and the desired standpipe pressure. A standpipe pressure control system for use in a drilling operation can include a controller which outputs an annulus pressure setpoint based on a comparison of a measured standpipe pressure to a desired standpipe pressure, and a choke which is automatically adjusted in response to the annulus pressure setpoint. A well system can include a standpipe line connected to a drill string in a wellbore, a sensor which measures pressure in the standpipe line, and a controller which outputs an annulus pressure setpoint based at least in part on a difference between the measured pressure and a desired standpipe pressure.

Abstract: An apparatus includes a body having a central axis, a fluid inlet coupled to the body, the fluid inlet being adapted to receive a flow of a fluid, and a fluid outlet coupled to the body. The fluid inlet and the fluid outlet are substantially coaxially aligned so as to define a flow axis through the apparatus, and the flow axis is laterally offset from and perpendicular to the central axis of the body. A rotating blade assembly is disposed within said body and includes a plurality of blades, wherein the rotating blade assembly is adapted to be controllably rotated about the central axis so as to control a fluid level of the flow of fluid entering the fluid inlet.

Abstract: A method for a pressure release encoding system for communicating downhole information through a wellbore to a surface location includes positioning a valve and a brake in a drilling mud circulation system, initiating flow of drilling mud through the system, sensing flow through the valve and setting the brake at predefined pressure levels, sensing downhole conditions and releasing corresponding percentages of pressure across the valve at time intervals, and determining the downhole conditions at the surface by analyzing those associated time intervals. The method includes activation of the encoding system using drilling mud flow and setting predefined pressure levels, so that the pressure drops in the encoding process are from predefined levels at equilibrium and independent of fluid flow.

Abstract: An arrangement in a rock drill rig 10 has an inlet valve 31 arranged upstream from a displacement compressor 32 that is used for supplying an air flow 34 to at least one flushing hole 23 in the surface of a drill bit 20. The rock drill rig 10 also has an air regulator 35 arranged to regulate the system pressure in the air flow path 34 downstream from the compressor and a detector for detecting air flow through the at least one flushing hole 23 in the surface of the drill bit. The detector has a pressure sensor 36, arranged between the air regulator 35 and the inlet valve 31, for measuring the reduced system pressure.

Abstract: A method for controlling flow of fluid from an annular space in a wellbore includes changing a flow restriction in a fluid flow discharge line from the wellbore annular space. The flow restriction is changed at a rate related to a difference between at least one of a selected fluid flow rate out of the wellbore and an actual fluid flow rate out of the wellbore, and a selected fluid pressure in the annular space and an actual pressure in the annular space.

Abstract: An apparatus for continuously flowing drilling fluid along a drill string includes a continuous circulation device having at least a first fluid path in fluid communication with a top drive and a second fluid path in communication with a diverter. The diverter is in selective fluid communication with a pipe stand associated with the drills string. The apparatus also includes at least one sensor that estimates at least one operating parameter associated with the continuous circulation device. A related method includes using a continuous circulation device as described to manipulate the drill string and controlling the continuous circulation device using at least one sensor configured to estimate at least one operating parameter associated with the continuous circulation device.

Abstract: A downhole tool includes a downlinking system deployed in a downhole tool body having an internal through bore. The downlinking system includes a differential pressure transducer configured to measured a pressure difference between drilling fluid in the internal through bore and drilling fluid external to the tool (in the borehole annulus). The differential transducer is electrically connected with an electronic controller (deployed substantially anywhere in the drill string) that is configured to receive and decode pressure waveforms.

Abstract: Cleanup monitoring and prediction in real time targeting estimation of pumpout volume versus final contamination, including detecting breakthrough of formation fluid to a sampling tool and detecting transition of cleanup regime from a predominantly circumferential cleanup regime to a predominantly vertical cleanup regime. Similar workflow can be employed for estimating contamination at the end of cleanup production for a given pumpout volume.

Abstract: A method and system to aid and/or train well control personnel by measuring the actual hydraulic delay and pressure attenuation of operator choke changes during well control operations or simulations. This provides the choke operator with an anticipated drillpipe pressure as soon as the choke is adjusted, accounting for hydraulic delay, pressure attenuation and prior choke adjustments that are currently travelling through the wellbore as well as reflections of the transient pressure waves against the pumps and choke. The technique that is described utilizes only three inputs, and works without knowledge of or inputting data such as well depth, pipe and hole geometry, mud properties, temperature, water depth, land, offshore platform or floating (subsea BOP's) drilling rigs. Further, the system can detect and warn the operator of potential problems based on the results of the real time analysis.

Abstract: Multiple sensors on a drill string can be utilized to perform equivalent circulation density (ECD) analysis. By utilizing multiple ones of the sensors, the pressure drop in each section of the wellbore can be classified. Additionally, the inclusion of multiple sensors in the drill string allows a wellbore to be sectioned into intervals bounded by any two sensors. Pressure events occurring in a single section of the wellbore bounded by any two sensors can be isolated and analyzed. The isolation can be achieved by subtracting the pressure measured on the shallower sensor from that measured on the deeper sensor.

Abstract: Multiple sensors in a wellbore can be utilized in a high density sweep analysis. In particular, annular pressures, recorded by the multiple sensors as the sweep is circulated, can be utilized to analyze the performance of a high density sweep. The high density sweep analysis can be used to create a prediction of the impact of circulating a high density sweep. The high density sweep analysis can calculate the position of the high density sweep in the well during the circulation by utilizing the multiple sensors and derive information about the presence of solids in the well, their likely location and whether or not the wellbore is clean prior to tripping out of the well.

Abstract: An apparatus and method for producing pressure signals which indicate when weight-on-bit, during the drilling of a wellbore, exceed a predetermined, upper limit. The apparatus includes a first mandrel and a second mandrel that inserts into and is axially moveable within the first mandrel. The position of the second mandrel may be dependent upon the balance of a biasing member's biasing strength and the weight-on-bit exerted on the drill bit. If weight-on-bit values overcome the biasing strength of the biasing member, the second mandrel may move uphole within the first mandrel and create a pressure signal that is detectable at surface so that the operator is made aware that weight-on-bit values exceed the upper limit.

Abstract: An apparatus for measuring permittivity of a sample. The apparatus includes: a sample chamber including a sealed space portion in which a sample to be measured is put; a pressure adjusting unit for varying pressure by applying water pressure to the space portion of the sample chamber; a permittivity sensor for measuring permittivity of the sample and disposed outside the sample chamber; measurement conducting wires including conductors, installed to contact the sample and connected to the permittivity sensor by using electric wires; and a data logger for storing data relating to permittivity that is measured by the permittivity sensor.

Abstract: A method of identifying a self-sustained influx of formation fluids into a wellbore includes the steps of closing an annular shut-off device and diverting an annular return flow from the wellbore through a first flow rate measurement device, measuring a flow rate of said annular return flow, measuring an inlet flow rate of fluids entering the well through a second flow rate measurement device in a fluid injection line, and identifying a self-sustained influx of formation fluids if a non-decreasing measured annular return flow rate is greater than said measured inlet flow rate.

Abstract: A mud pulser tool to be positioned into a downhole environment is disclosed. The mud pulser tool includes a control valve that is selectively opened to allow fluid to flow through the mud pulser tool or selectively closed to restrict the fluid flow, wherein the control valve is selectively opened or closed to produce a mud pulse signal transmitted through the fluid. The mud pulser tool also includes a sensor system to measure a pressure drop across the control valve. In one example, the mud pulser tool includes a control system to selectively open or close the control valve to adjust the pressure drop to produce a selected pressure drop across the control valve.

Abstract: A method of drilling a subterranean borehole comprising: a) pumping a drilling fluid down a drillstring (12), the drillstring (12) having a bit (14) at an end thereof, b) rotating the drillstring (12) about its longitudinal axis so that the bit forms a borehole (10) in the ground, the method further comprising the steps of: c) determining a desired drilling fluid flow rate range d) determining the desired upper and lower limits of the fluid pressure at the bottom of the wellbore (the BHP); e) determining the viscosity of drilling fluid which will maintain the BHP within the range set by the upper and lower BHP limits over the entire or the majority of the required drilling flow rate range; f) adjusting the composition of a drilling fluid to bring the drilling fluid to the viscosity calculated in step e above.

Abstract: A method for predicting a pressure window for drilling a borehole in a formation includes: obtaining a pore pressure related data value of the formation using a data acquisition tool; predicting pore pressure uncertainty from the pore pressure related data value of the formation using a processor; estimating uncertainty of a pressure window for drilling fluid using the predicted pore pressure uncertainty using a processor; and applying the estimated uncertainty to the pressure window to provide a modified pressure window using a processor.

Abstract: A method of drilling a subterranean well bore using a tubular drill string described. One embodiment of the method includes the steps of injecting a drilling fluid into the well bore via the drill string and removing said drilling fluid from an annular space in the well bore around the drill string via a return line. The method can also include oscillating the pressure of the fluid in the annular space in the well bore, and monitoring the rate of flow of fluid along the return line.

Abstract: Systems, apparatus and methods are described for purposes of initiating a response to detection of an adverse operational condition involving a system including a drill rig and an inground tool. The response can be based on an uphole sensed parameter in combination with a downhole sensed parameter. The adverse operational condition can involve cross-bore detection, frac-out detection, excessive downhole pressure, a plugged jet indication and drill string key-holing detection. A communication system includes an inground communication link that allows bidirectional communication between a walkover detector and the drill rig via the inground tool. Monitoring of inground tool depth and/or lateral movement can be performed using techniques that approach integrated values. Bit force based auto-carving is described in the context of an automated procedure.

Abstract: A method of selectively actuating a downhole tool, wherein the downhole tool includes a tubular body with an axial borehole therethrough and at least one component, includes increasing a flow rate of a circulating fluid in the axial borehole of the downhole tool to reach a specified circulating fluid pressure, detecting an increased circulating fluid pressure in the borehole of the tool with at least one sensor, actuating a motor to operate a pump, and sending a fluid to operate a sliding sleeve. The method further includes operating the sleeve disposed in the axial borehole to open an actuation chamber port in response to the increased circulating fluid pressure in the borehole of the tool, thereby filling an actuation chamber with the drilling fluid, and moving the at least one expandable component radially outward.

Abstract: A new approach to measuring the gases present in the drilling fluid, or “mud”, while drilling oil and gas wells and analyzing the mud at the well surface. The method replaces inconsistent legacy measurements which mix the formation gases with air arbitrarily and report inconsequential values called “units, Equivalent Methane in Air.” This method instead expresses gas values in terms of Volume of Gas Per Volume of Mud, producing values of universal meaning that everyone can standardize upon. The method further improves gas measurement by expressing gas content using the several energy values of the gases. The resulting standard is a summation measurement of the energy of all gas components present, not limited to Methane. The end result is a gas concentration value that is made universally consistent across many logs made at different times in any location or formation.

Abstract: According to one aspect, a digital display unit includes a microcontroller to process digital information received from one or more sensors, a display, and a switch in electrical communication with the microcontroller so that the microcontroller displays an output on the display that is specific to a type of sensor. The type of sensor may be selected from a position sensor, a pressure sensor, and a stroke counter. The digital display unit may be part of a choke control panel. The microcontroller and the display may be disposed in an enclosure, and an electrical power source may be disposed in the enclosure to supply electrical power to the microcontroller and the one or more sensors. A digital hydraulic choke position sensor assembly and a digital pressure sensor assembly are also described, one or both of which may be used in a system for drilling an oil or gas well.

Abstract: A drilling system including a drill string (12) which extends into a borehole (10), and a well closure system which contains fluid in the annular space (16) in the borehole around the drill string, the well closure system having a side bore whereby controlled flow of fluid out of the annular space in the borehole around the drill string is permitted, the side bore being connected to fluid return line (28) which extends from the side bore to a fluid reservoir (34), there being provided in the fluid return line a valve (30a) which is operable to restrict flow of fluid along the fluid return line to variable extent, and a flow meter (32) operable to measure the rate of flow of fluid along the fluid return line, the flow meter being located between the valve and the side bore, wherein a filter (40) is provided between the flow meter and the side bore, the filter including a plurality of apertures which have a smaller cross-sectional area than the smallest fluid flow lines in the flow meter.

Abstract: A method for determining existence of a borehole fluid control event by controlling formation pressure during the drilling of a borehole includes selectively pumping a drilling fluid through a drill string extended into a borehole, out a drill bit at the bottom end of the drill string, and into an annular space between drill string and the borehole. The drilling fluid leaves the annular space proximate the surface. Existence of a well control event is determined when at least one of the following events occurs: the rate of the selective pumping remains substantially constant and the annular space pressure increases, and the rate of the selective pumping remains substantially constant and the annular space pressure decreases.

Abstract: An apparatus for wireless communications in a drilling operations environment can include an instrument hub that is inline with drill pipe of a drill string. The instrument hub includes a sensor to receive downhole communications from downhole. The instrument hub also includes a transmitter to wireless transmit data representative of the downhole communications to a data processor unit.

Abstract: A method of controlling pressure in a mud pump system includes generating a pressure limiting factor output using a pressure feedback input and a motor speed input to calculate a fluid conductance estimate, maintaining the pressure limiting factor output at a maximum value based on a pressure set-point, continuously updating a normal fluid conductance value based on the fluid conductance estimate while the pressure limiting factor output remains at the maximum value, freezing the normal fluid conductance value, if the pressure limiting factor output is less than the maximum value, calculating a change in fluid conductance based on the normal fluid conductance value and the fluid conductance estimate, generating at least one adaptive gain based on the change in fluid conductance, and controlling a motor speed of a pump in the mud pump system based on the at least one adaptive gain.

Abstract: A system and a method may determine formation strength of a well. The system and the method may use pressure measurements and temperature measurements to determine controlled fracture pressures before the uncontrolled fracture pressure is reached. The system and the method may use pressure measurements and temperature measurements to determine closure stresses while drilling and may use the closure stresses with core and log measurements to optimize a hydraulic stimulation program.

Abstract: A method for maintaining pressure in a wellbore during drilling operations includes the steps of providing fluid from a reservoir through a drill string, circulating the fluid from the drill string to an annulus between the drill string and the wellbore, isolating pressure in the annulus, measuring pressure in the annulus, calculating a set point backpressure, applying back pressure to the annulus based on the set point back pressure, diverting fluid from the annulus to a controllable choke, controllably bleeding off pressurized fluid from the annulus, separating solids from the fluid, and directing the fluid back to the reservoir. An apparatus for maintaining pressure in a wellbore during drilling operations includes an adjustable choke for controllably bleeding off pressurized fluid from the wellbore annulus, a backpressure pump for applying a calculated set point backpressure, and a processor for controlling the adjustable choke and backpressure pump.

Abstract: A pressure release encoding system for communicating downhole information through a wellbore to a surface location include a downhole tool with a valve for providing a fluid restriction to fluid passing in the wellbore, a sensor positioned in the wellbore for sensing a downhole condition in the wellbore, a brake cooperative with the valve for moving the valve between at least two positions in timed relation to the downhole condition sensed by the sensor, and a detector positioned at the surface location for providing a measurement value at the surface location correlative to the time between the changes of the pressure of the fluid in the wellbore. The system associates position of the valve with pressure transduction. The sensor is an inclination sensor for sensing an angle of inclination of the wellbore.

Abstract: A method of monitoring a well for unwanted formation fluid influx is disclosed. Measurements of well outflow are acquired during a period in which drilling operations are performed for the well. Occurrences of stagnant flow events during the period are determined. An outflow signature is generated from the well outflow measurements for each stagnant flow event. The outflow signatures are displayed sequentially in time of occurrence. Each outflow signature is analyzed for an anomaly.

Abstract: An apparatus and method for reducing temperature along a bottomhole assembly during a drilling operation is provided. In one aspect the bottomhole temperature may be reduced by drilling a borehole using a drill string having a bottomhole assembly at an end thereof, circulating a fluid through the drill string and an annulus between the drill string and the borehole, diverting a selected portion of the fluid from the drill string into the annulus at a selected location above the drill bit to reduce pressure drop across at least a portion of the bottomhole assembly to reduce temperature of the bottomhole assembly during the drilling operation.

Abstract: An illustrative embodiment of a method is disclosed for assessing image quality of a down hole formation image, the method comprising collecting acquisition system data from a plurality of sensors down hole; applying a set of rules to the acquisition system data to obtain an acquisition quality indicator; and presenting the acquisition quality indicator at a surface location. A system is disclosed for performing the method.

Abstract: A method of controlling pressure in a well can include transmitting an instruction to change flow through an annulus formed radially between a drill string and a wellbore, and adjusting a pressure setpoint in response to the transmitting. A well drilling system can include a flow control device which varies flow through a drill string, and a control system which changes a pressure setpoint in response to an instruction for the flow control device to change the flow through the drill string. A method of controlling pressure in a well can include transmitting an instruction to divert flow from a drill string, and adjusting a pressure setpoint in response to the transmitting.

Abstract: A system and method for determining at least one fluid characteristic of a downhole fluid sample using a downhole tool are provided. In one example, the method includes performing a calibration process that correlates optical and density sensor measurements of a fluid sample in a downhole tool at a plurality of pressures. The calibration process is performed while the fluid sample is not being agitated. At least one unknown value of a density calculation is determined based on the correlated optical sensor measurements and density sensor measurements. A second optical sensor measurement of the fluid sample is obtained while the fluid sample is being agitated. A density of the fluid sample is calculated based on the second optical sensor measurement and the at least one unknown value.

Abstract: A method for detecting a wellbore influx with drill string distributed measurements includes obtaining a first annular measurement from a first sensor disposed on a drill string. The method also includes obtaining a second annular measurement from a second sensor disposed on the drill string and computing a gradient of a first interval defined by the first and second sensors. Finally, the method includes detecting a wellbore influx based on the gradient and the first and second annular measurements.

Abstract: A downhole tool includes a downlinking system deployed in a downhole tool body having an internal through bore. The downlinking system includes a differential pressure transducer configured to measured a pressure difference between drilling fluid in the internal through bore and drilling fluid external to the tool (in the borehole annulus). The differential transducer is electrically connected with an electronic controller (deployed substantially anywhere in the drill string) that is configured to receive and decode pressure waveforms.

Abstract: Methods and apparatus to determine slowness of drilling fluid in an annulus are described. An example method of determining slowness of drilling fluid in an annulus of a borehole in a formation includes obtaining a first slowness of the drilling fluid in the annulus and measuring with a downhole tool slownesses of the formation based on the first slowness. The example method also includes determining a first compressibility of the formation based on the slownesses of the formation and a first density of the formation and calculating a second density and a second compressibility of the drilling fluid in the annulus based on the first density and the first compressibility. The method also includes calculating a second slowness of the drilling fluid in the annulus based on the second density and the second compressibility.

Abstract: A method of drilling a subterranean well bore using a tubular drill string, the method including the steps of injecting a drilling fluid into the well bore via the drill string and removing said drilling fluid from an annular space in the well bore around the drill string via a return line, wherein the method further includes oscillating the pressure of the fluid in the annular space in the well bore, and monitoring the rate of flow of fluid along the return line.

Abstract: An apparatus uses well devices, both downhole and at the surface, to control at least one condition in a wellbore. The downhole equipment includes flow restriction devices that modulate fluid flow along a wellbore annulus, flow bypass devices that selectively bypass fluid flow from wellbore tubular bore to the wellbore annulus, and downhole sensors that generate information relating to a selected parameter of interest. The surface equipment includes a pump that circulates a drilling fluid in the wellbore. Controllers, which may be downhole and/or at the surface, use sensor information to generate advice parameters or signals that may be used to control the flow restriction devices, the flow bypass devices, and/or the fluid circulation pump.

Abstract: A method of drilling a subterranean well bore using a tubular drill string is described. One embodiment of the method includes the steps of injecting a drilling fluid into the well bore via the drill string and removing the drilling fluid from an annular space in the well bore around the drill string via a return line. The method can also include oscillating the pressure of the fluid in the annular space in the well bore, and monitoring the rate of flow of fluid along the return line.

Abstract: A tunneling apparatus is disclosed. The tunneling apparatus includes a drill string formed by a plurality of drill string sections. The drill string has a proximal end and a distal end. The tunneling apparatus also includes a drill head mounted at the distal end of the drill string, the drill head including a cutting unit, a rotational driver that provides torque for rotating the cutting unit, and a thrust driver for applying thrust to the drill string. The tunneling apparatus further includes a vacuum system for withdrawing spoils generated by the cutting unit during operation of the tunneling apparatus and a drilling fluid system for providing drilling fluid to adjacent the cutting unit during operation of the tunneling apparatus. The tunneling apparatus includes a control system that allows an operator to select between a drilling mode and a break-out mode.

Abstract: A Drill-To-The-Limit (DTTL) drilling method variant to Managed Pressured Drilling (MPD) applies constant surface backpressure, whether the mud is circulating (choke valve open) or not (choke valve closed). Because of the constant application of surface backpressure, the DTTL method can use lighter mud weight that still has the cutting carrying ability to keep the borehole clean. The DTTL method identifies the weakest component of the pressure containment system, such as the fracture pressure of the formation or the casing shoe leak off test (LOT). With a higher pressure rated RCD, such as 5,000 psi (34,474 kPa) dynamic or working pressure and 10,000 psi (68,948 kPa) static pressure, the limitation will generally be the facture pressure of the formation or the LOT. In the DTTL method, since surface backpressure is constantly applied, the pore pressure limitation of the conventional drilling window can be disregarded in developing the fluid and drilling programs.

Abstract: A method of controlling the annular pressure in a well during a well construction operation. The operation comprises pumping a fluid down a tubing located within the well and extracting the fluid that flows back through an annulus within said well and surrounding the tubing. The method comprises defining a set pressure pref, determining a desired extraction flow rate qc of fluid from said annulus in dependence upon the set pressure pref and a pumped flow rate into the annulus, and configuring an extraction path to achieve said desired extraction flow rate.

Abstract: A method for reducing temperature of a bottomhole assembly during a drilling operation is disclosed, that, in one aspect, may include: drilling a borehole using a drillstring including a bottomhole assembly by circulating a fluid through the drillstring and an annulus between the drillstring and the borehole, pausing drilling, continuing circulating the fluid through the dill string and the annulus. The method further includes diverting a portion of the fluid from the drillstring into the annulus at a selected location above the drill bit to reduce temperature of the bottomhole assembly.

Abstract: A method for characterizing a subsurface formation using a fluid pressure response during wellbore drilling operations includes the steps of determining a change in wellbore pressure proximate the surface, calculating a change in volumetric flow rate out of the wellbore as a function of the change in wellbore pressure proximate the surface, determining a downhole fluid pressure in the wellbore corresponding to the change in wellbore pressure proximate the surface and determining a productivity index value as a function of the change in volumetric flow rate, the downhole fluid pressure and a reservoir pressure.

Abstract: Embodiments of systems, program product, and methods for controlling drilling fluid pressures are provided. These embodiments, for example, can provide dynamic density control with highly adaptive, real-time, process-control and are scalable to any rig, large or small, on land or water. Combined static and dynamic stresses and displacements can be determined continuously at strategic locations in and around the wellbore of a well so that insitu and operational induced pressure window limitations at specific weak-points or other locations of interest are controlled.

Abstract: A method and apparatus used to transmit information to the surface from a subsurface location during the process of drilling a bore hole is described. A novel pressure pulse generator or “pulser” is coupled to a sensor package, a controller and a battery power source all of which reside inside a short section of drill pipe close to the bit at the bottom of the bore hole being drilled. The assembled apparatus or “MWD Tool” can be commanded from the surface to make a measurement of desired parameters and transmit this information to the surface by encoding data in pressure pulses generated by a pulser valve that includes a stator and a rotor which may be open and closed to create pressure pulses.

Abstract: The method of controlling the load on a drill bit drilling a hole by providing differential pressure across a seal area on a drilling assembly to increase the bit load and providing a relief valve from the annular area above the seal to the bore returning fluid to the surface to limit the maximum differential pressure to limit the maximum load allowed.