METHODS FOR MONITORING WELL CEMENTING OPERATIONS

Abstract

Cement placement simulations and post-placement simulations are traditionally performed before the cementing operation takes place. Several simulation iterations may be performed, allowing engineers to develop an optimal cement treatment design. When the cementing operation takes place, engineers may follow the procedure prescribed by the simulator. After the operation is complete and the cement has set, logging operations may be performed to verify that the goals of the cementing operation have been met. Monitoring the progress of the cementing operation in real time allows a determination of whether cementing events are unfolding as predicted by the simulator. If deviations from the plan occur, some real-time adjustments may be made to improve cementing results.

Description

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

The present disclosure broadly relates to methods for monitoring well cementing operations. In particular, the methods relate to monitoring well cementing parameters and comparing the parameters to cement placement simulations in real time.

Primary cementing is a technique for placing cement slurries in the annular space between the casing and the borehole. After placement, the cement hardens to form a hydraulic seal in the wellbore, preventing the migration of formation fluids in the annulus. Therefore, primary cementing is one of the most important stages during the drilling and completion of a well. This procedure must be planned and executed carefully, as there is but one chance to complete the job successfully.

In addition to providing zonal isolation, the set cement sheath should anchor and support the casing string (preventing formation sloughing or caving into the wellbore) and protect the casing string against corrosion by formation fluids. Uncemented steel casing can corrode rapidly when exposed to hot formation brines and hydrogen sulfide. It can also be subjected to erosion by the high velocity of produced fluids, particularly when solid particles such as formation sand are being transported. Lateral loads on poorly cemented casing strings can result in buckling or collapse because of overloading at certain points. On the other hand, properly cemented casing is subjected to a nearly uniform loading approximately equal to the overburden pressure.

In principle, primary cementing techniques are the same regardless of casing-string purpose and size. The cement slurry is pumped down inside the string to be cemented, exits the bottom, and displaces drilling mud as it moves up the annulus. Or, a “reverse cementing” technique may be performed wherein fluids are pumped in the opposite direction—down the annulus and up the casing.

Pumping dense fluids such as cement slurries down a casing string can result in a phenomenon known as free-fall or U-tubing. The fluids inside the casing and in the annulus will naturally tend to achieve a hydrostatic-pressure equilibrium. During the course of the cement job, some interesting effects may be observed.

The density of cement slurries is usually higher than those of the drilling fluid, chemical wash or spacer. When the cement slurry is introduced inside the casing, a hydrostatic pressure imbalance is created between the inside of the casing and the annulus. As a result, the cement slurry has a tendency to “free-fall” and draws a vacuum inside the upper part of the casing.

In many cementing operations, the pump rate into the casing, Q_in, is insufficient to keep the casing full during the early part of the job. This results in a net flow or efflux of fluid from the well. The rate of efflux, Q_out, may be much greater than Q_in. Eventually, as hydrostatic pressure equilibrium is approached, Q_out falls below Q_in and the casing gradually refills. At some point, Q_out may reach zero and the fluid column in the annulus may become stationary. Such events are easily misinterpreted as partial or complete loss of circulation. Finally, when the casing is again full of fluid, Q_in and Q_out will be equal. However, these values may not remain so for the remainder of the job. If a low-density wash is present, it may cause an annular-pressure reduction as it flows past the casing shoe. This will in turn cause a second period of free-fall, accompanied by another surge of high returns. The beginning and end of a U-tubing event can easily be detected by measuring the surface pressure during the cement job

Considering the importance of annular fluid velocities and pressures to the safe and successful execution of a cement job, it is clear that U-tubing must be considered in any job design. Algorithms exist that permit accurate simulations of these phenomena. These algorithms have been validated against carefully measured field parameters during cementing operations.

Computer simulators are also used to determine the number of centralizers on a casing string to achieve optimal standoff and encourage complete removal of drilling fluids from the annulus. Other factors that the simulators consider in their calculations include temperature, wellbore geometry, formation fracture gradients, mud conditioning, rheological properties of cementing fluids (e.g., mud, chemical washes, spacer fluids and cement slurries), casing movement via reciprocation and rotation and pump rates.

The simulators may generate several predictions, including mud displacement, cement slurry coverage, flow rates, temperature and pressure evolution at various locations in the well and well control. One such simulator is CEMENTICS, available from Schlumberger.

Further information about well cementing operations and simulators may be found in the following publications.

Piot B: “Primary Cement Job Design,” in Nelson E B and Guillot D (eds.): Well Cementing-2nd Edition, Houston: Schlumberger (2006): 435-458.

Piot B and Cuvillier G: “Primary Cementing Techniques,” in Nelson E B and Guillot D (eds.): Well Cementing-2 nd Edition, Houston: Schlumberger (2006): 459-501.

SUMMARY

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

The present disclosure reveals methods relating to monitoring well cementing parameters and comparing the parameters to cement placement simulations in real time. Additionally, adjustments to the cementing operation may be performed in real time in response to operational deviations from the simulation predictions.

In an aspect, embodiments relate to methods for cementing a subterranean well. A cement slurry is prepared and pumped into the well through a casing interior. After exiting the casing interior at the bottom of the casing string, the slurry is pumped through an annulus between the casing string exterior and a borehole wall. During the operation, real-time of cementing parameters takes place. The parameters may be temperature, pressure or return rate or a combination thereof. The real-time monitored parameters are then compared to a previously generated cement placement simulation, or a previously generated post-placement simulation or both.

In a further aspect, embodiments relate to methods for confirming cement-placement events. A cement slurry is prepared and pumped into the well through a casing interior. After exiting the casing interior at the bottom of the casing string, the slurry is pumped through an annulus between the casing string exterior and a borehole wall. During the operation, real-time of cementing parameters takes place. The parameters may be temperature, pressure or return rate or a combination thereof. The real-time monitored parameters are then compared to a previously generated cement placement simulation, or a previously generated post-placement simulation or both.

In yet a further aspect, embodiments relate to methods for confirming cement-placement events. A cement slurry is prepared and pumped into the well through a casing interior. After exiting the casing interior at the bottom of the casing string, the slurry is pumped through an annulus between the casing string exterior and a borehole wall. During the operation, real-time monitoring of cementing parameters takes place. The parameters may be pump rate, pressure, fluid volume, fluid density or fluid temperature or a combination thereof. The real-time monitored parameters are then entered into a cement placement simulator, and the simulator is allowed to predict future cement placement events.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a well diagram showing the location of sensors that are employed in the disclosed methods.

DETAILED DESCRIPTION

At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation—specific decisions are made to achieve the developer's specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. In addition, the composition used/disclosed herein can also comprise some components other than those cited. In the summary of the disclosure and this detailed description, each numerical value should be read once as modified by the term “about” (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. The term about should be understood as any amount or range within 10% of the recited amount or range (for example, a range from about 1 to about 10 encompasses a range from 0.9 to 11). Also, in the summary and this detailed description, it should be understood that a concentration range listed or described as being useful, suitable, or the like, is intended that any concentration within the range, including the end points, is to be considered as having been stated. For example, “a range of from 1 to 10” is to be read as indicating each possible number along the continuum between about 1 and about 10. Furthermore, one or more of the data points in the present examples may be combined together, or may be combined with one of the data points in the specification to create a range, and thus include each possible value or number within this range. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to a few specific, it is to be understood that inventors appreciate and understand that any data points within the range are to be considered to have been specified, and that inventors possessed knowledge of the entire range and the points within the range.

Cement placement simulations and post-placement simulations are traditionally performed before the cementing operation takes place. Several simulation iterations may be performed, allowing engineers to develop an optimal cement treatment design. When the cementing operation takes place, engineers may follow the procedure prescribed by the simulator. After the operation is complete and the cement has set, logging operations may be performed to verify that the goals of the cementing operation have been met.

Applicant has determined that advantages may be gleaned by monitoring the progress of the cementing operation in real time, thereby allowing a determination of whether cementing events are unfolding as predicted by the simulator. If deviations from the plan occur, some real-time adjustments may be made to improve cementing results.

In an aspect, embodiments relate to methods for cementing a subterranean well. A cement slurry is prepared and pumped into the well through a casing interior. After exiting the casing interior at the bottom of the casing string, the slurry is pumped through an annulus between the casing string exterior and a borehole wall. During the operation, real-time monitoring of cementing parameters takes place. The parameters may be temperature, pressure or return rate or a combination thereof. The real-time monitored parameters are then compared to a previously generated cement placement simulation, or a previously generated post-placement simulation or both.

The cement placement events may comprise landing of a cementing plug, landing of a cementing dart, passage of a fluid interface past a given location in a well, setting of the cement slurry, or arrival of a cement slurry at a given location in the well, or combinations thereof.

In a further aspect, embodiments relate to methods for confirming cement-placement events. A cement slurry is prepared and pumped into the well through a casing interior. After exiting the casing interior at the bottom of the casing string, the slurry is pumped through an annulus between the casing string exterior and a borehole wall. During the operation, real-time monitoring of cementing parameters takes place. The parameters may be temperature, pressure or return rate or a combination thereof. The real-time monitored parameters are then compared to a previously generated cement placement simulation, or a previously generated post-placement simulation or both.

In yet a further aspect, embodiments relate to methods for confirming cement-placement events. A cement slurry is prepared and pumped into the well through a casing interior. After exiting the casing interior at the bottom of the casing string, the slurry is pumped through an annulus between the casing string exterior and a borehole wall. During the operation, real-time monitoring of cementing parameters takes place. The parameters may be pump rate, pressure, fluid volume, fluid density or fluid temperature or a combination thereof. The real-time monitored parameters are then entered into a cement placement simulator, and the simulator is allowed to predict future cement placement events.

The cement placement events may comprise landing of a cementing plug, landing of a cementing dart, passage of a fluid interface past a given location in a well, setting of the cement slurry, or arrival of a cement slurry at a given location in the well, or combinations thereof.

A cement placement simulation may or may not have been performed before pumping the slurry into the well.

For each aspect, temperature sensors may be located at a wellhead, at a casing shoe, along fibers installed throughout the well, or at a return line or a combination thereof.

For each aspect, pressure sensors may be located at a wellhead, at a casing shoe, along fibers installed throughout the well, or at a return line or a combination thereof.

For each aspect, flow rate sensors may be located at a wellhead, at a casing shoe, along fibers installed throughout the well, at a mud pit, or at a return line or a combination thereof.

For each aspect, the monitored parameters may be synchronized and displayed together on a computer screen.

For each aspect, the post-placement simulation may employ calorimetry data to provide a post-placement well temperature prediction.

For each aspect, the monitored parameters may provide a real-time prediction of when the cement slurry will reach a given location in the well.

For each aspect, the parameters may be monitored at a wellsite or from a remote location.

For each aspect, the cement placement simulation may include a U-tube simulator.

For each aspect, the monitored parameters may provide a real-time prediction of when the cement slurry will reach a given location in the well.

For each aspect, the telemetry between the sensors and the receivers may be transmitted along wires, optical fibers or wirelessly or a combination thereof. Wireless communication may be in the form of electromagnetic signals, acoustic signals or both.

A non-limiting embodiment of the disclosure is portrayed in FIG. 1. An example well 100 comprises several elements: a wellhead 101, a casing string 102, a casing shoe 103, a return line 104, a mud pit 105, a fiber cable 106 placed along the casing string 102, a temperature sensor 107, a pressure sensor 108 and a flow rate sensor 109. Although the sensors 107-109 are shown only at the casing shoe 102, they may also be located at the wellhead 101, along the fiber cable 106, at the return line 104 or at the mud pits or a combination thereof.

Although various embodiments have been described with respect to enabling disclosures, it is to be understood that this document is not limited to the disclosed embodiments. Variations and modifications that would occur to one of skill in the art upon reading the specification are also within the scope of the disclosure, which is defined in the appended claims.

Claims

1. A method for cementing a subterranean well, comprising:

(i) preparing a cement slurry;

(ii) pumping the slurry into the well through a casing interior and, after exiting the casing interior, through an annulus between a casing exterior and a borehole wall;

(iii) real-time monitoring of parameters comprising temperature, pressure or return rate or a combination thereof; and

(iv) comparing the real-time monitored parameters to a previously generated cement placement simulation or a previously generated post-cement placement simulation or both.

2. The method of claim 1, wherein temperature sensors are located at a wellhead, at a casing shoe, along fibers installed throughout the well, or at a return line or a combination thereof.

3. The method of claim 1, wherein pressure sensors are located at a wellhead, at a casing shoe, along fibers installed throughout the well, or at a return line or a combination thereof.

4. The method of claim 1, wherein flow rate sensors are located at a wellhead, at a casing shoe, along fibers installed throughout the well, at a mud pit, or at a return line or a combination thereof.

5. The method of claim 1, wherein the monitored parameters are synchronized and displayed together on a computer screen.

6. The method of claim 1, wherein the post-placement simulation employs calorimetry data to provide a post-placement well temperature prediction.

7. The method of claim 1, wherein the monitored parameters provide a real-time prediction of when the cement slurry will reach a given location in the well.

8. A method for confirming cement-placement events, comprising:

(i) preparing a cement slurry;

(ii) pumping the slurry into a well through a casing interior and, after exiting the casing interior, through an annulus between a casing exterior and a borehole wall;

(iii) real-time monitoring of parameters comprising temperature, pressure or return rate or a combination thereof; and

(iv) comparing the real-time monitored parameters to a previously generated cement placement simulation or a previously generated post-cement placement simulation or both.

9. The method of claim 8, wherein temperature sensors are located at a wellhead, at a casing shoe, along fibers installed throughout the well, or at a return line or a combination thereof.

10. The method of claim 8, wherein pressure sensors are located at a wellhead, at a casing shoe, along fibers installed throughout the well, or at a return line or a combination thereof.

11. The method of claim 8, wherein flow rate sensors are located at a wellhead, at a casing shoe, along fibers installed throughout the well, at a mud pit, or at a return line or a combination thereof.

12. The method of claim 8, wherein the monitored parameters are synchronized and displayed together on a computer screen.

13. The method of claim 8, wherein the post-placement simulation employs calorimetry data to provide a post-placement well temperature prediction.

14. The method of claim 8, wherein the cement-placement events comprise landing of a cementing plug, landing of a cementing dart, passage of a fluid interface past a given location in a well, setting of the cement slurry, or arrival of a cement slurry at a given location in the well, or combinations thereof.

15. A method for modifying a cement placement simulation, comprising:

(i) preparing a cement slurry;

(ii) pumping the slurry into a well through a casing interior and, after exiting the casing interior, through an annulus between a casing exterior and a borehole wall;

(iii) real-time monitoring of parameters comprising pump rate, pressure, fluid volume, fluid density or fluid temperature or combinations thereof;

(iv) entering real-time data into a cement placement simulator and allowing the simulator to predict future cement-placement events.

16. The method of claim 15, wherein a cement placement simulation has been performed before pumping the slurry into the well.

17. The method of claim 15, wherein a cement placement simulation has not been performed before pumping the slurry into the well, and future cement-placement events are predicted in real time.

18. The method of claim 15, wherein temperature sensors are located at a wellhead, at a casing shoe, along fibers installed throughout the well, or at a return line or a combination thereof.

19. The method of claim 15, wherein pressure sensors are located at a wellhead, at a casing shoe, along fibers installed throughout the well, or at a return line or a combination thereof.

20. The method of claim 15, wherein flow rate sensors are located at a wellhead, at a casing shoe, along fibers installed throughout the well, at a mud pit, or at a return line or a combination thereof.