Method of investigation of oil and gas-producing wells

Abstract

A method of determination of oil- and gas-productive layers in a well, includes performing a first logging in a well having a casing over a potentially promising depth of a well from a space inside the casing radially outwardly through the casing by sending transmitting signals into layers near the well and receiving reflected signals, with perforations in the casing and in the layers in condition of presence of a filtrate in the layers in the near-well zone, insulating the perforations in the layers from an interior of the well, maintaining the perforations of the layers insulated from the interior of the well over a time sufficient for migration of the filtrate away from the near-well zone and accumulating in the near-well zone of the layers oil or gas, performing a second logging in condition when the near-well zone of the layers no longer contains the filtrate but can contain oil or gas, and comparing the reflected signals obtained from the second logging with the reflected signals obtained from the first logging to determine the presence or absence of oil or gas in the layers within the potentially promising depths.

Description

BACKGROUND OF THE INVENTION

The present invention relates to the oil and gas industry, and more particularly to methods of determining oil- and gas-productive layers in wells.

A method of increasing efficiency of exploration of oil-containing layers in a well with a casing is known, which utilizes a technology of sand-jet slotting for opening of the layers. This method can increase oil and gas recovery from 1.5 to 10 times as compared with a known method of opening oil- and gas-containing layers with the use of a cumulative perforation.

The sand-jet slotting can be used in old wells which include not only stopped wells but also abandoned wells which are still accessible after drilling of insulating bridges. Such wells have underdeveloped oil and gas layers, which are abandoned after the depletion and flooding when their use become not cost effective. In order to make a decision whether it is commercially viable to use the sand-jet slotting, it is necessary to obtain information for evaluation of saturation of layers, location of fluids, and productivity and quantity of oil and gas in a certain radius around the well. The existing methods do not allow to determine oil and gas content in such wells in order to locate oil and/or gas away fro walls of the well into a zone beyond a range which allows the use of geophysical methods of investigation of wells.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a method, which significantly improves accuracy of determination of oil and/gas productive layers in wells.

In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a method of determination of oil- and gas-productive layers in a well, comprising the steps of performing a first logging in a well having a casing over a potentially promising depth of a well from a space inside the casing radially outwardly through the casing by sending transmitting signals into layers near the well and receiving reflected signals, with perforations in the casing and in the layer in condition of presence of a filtrate in the layers in the near-well zone; insulating the perforations in the layers from an interior of the well; maintaining the perforations of the layers insulated from the interior of the well over a time sufficient for migration of the filtrate away from the near-well zone and accumulation in the near-well zone of oil gas; performing a second logging but in condition when the near-well zone of the layers no longer contain the filtrate but instead contains oil or gas; and comparing the reflected signals obtained from the second logging with the reflected signals obtained from the first logging to determine the presence of oil gas in the layers within the potentially promising depth.

Another feature of the present invention resides, briefly stated, in a carrying out said first and second logging by neutron logging, determining neutron properties of the near-well zone of the layers for obtaining the reflected signals in the first neutron logging and obtaining the reflected signals in the second neutron logging, and comparing the signals of the second neutron logging with the signals of the first neutron logging.

Still another feature of the present invention resides in carrying out said insulating by introducing a cement solution between the casing and the layers for closing the perforations in the layers so as to interrupt a hydrodynamic communication between the layers and the interior of the well.

A further feature of the present invention resides, briefly stated, in that said maintaining of the perforations of the layers insulated includes maintaining it for a period of 1-3 months.

The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a step of the inventive method which involves logging in a well with a filtrate of a drilling solution,

FIG. 2 is a view showing the step of insulation of perforated layers from the interior of a well.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method of determination of oil- and gas-productive layers in a well in accordance with the present invention is performed in the following manner.

In a first step shown in FIG. 1 of the inventive method a logging is performed in a well which is identified with reference numeral 1. The well 1 extends through a plurality of layers 22 having old perforations 3. A casing 4 is arranged in the well 1 and has a plurality of perforations 5. The space between the casing 4 and the layers 2 is no longer completely insulated due to the fact that a ring in the space it is damaged, for example, by the cumulative perforation during an initial development of the layers, and therefore there is a hydrodynamic communication between the layers and the well. As a result the near-well zone 6 of the layers is filled with a filtrate of a drilling solution, which is shown schematically and identified with reference numeral 7.

The logging is performed by a method which is effective in wells provided with the casing. A logging equipment identified with reference numeral 8 is introduced into a space inside the casing 4 and moved downwardly over a potentially prospective depth of the well. During this lowering of the equipment 8, in a plurality of points a signal transmitting part 9 of the equipment transmits signals into the near-well zone 6 of the layers 2, while a signal receiving part 10 of the equipment 8 receives signals reflected from the near-well zone of the layer 2. The reflected signals are indicative of properties of the near-well zone of the layers and can provide an initial indication of presence or absence of oil and/or gas.

In the next step of the inventive method shown in FIG. 2 the hydrodynamic communication between the perforations of the near-well zone 6 of the layers 2 and the interior of the well through perforations 5 of the casing 4, is interrupted. For this purpose a concrete solution 11 is introduced into the interior of the column 4, penetrates through the perforations 5 of the column 4, penetrates into a space between the casing 4 of the layers 2 and provides an uninterrupted concrete ring around the casing, so that there is no longer any communication between the perforations of the layers and the interior of the well.

Then the well is closed for a certain time, for example 1 and 3 months depending on the nature of the layers, for the purpose of displacement of the filtrate 7 of the drilling solution away from the near-well zone 6 of the layers 2. When the filtrate 7 of the drilling solution moves away from the near-well zone 6 of the layers, a fluid 12, in particular, oil gas saturates the near-well zone of the layers.

Then a second logging is performed. It is carried out with the same logging equipment and in the same manner, with the signal transmitting part 9 sending signals into the near-well zone 6 of the layers 2 and the signal receiving part 10 receiving the reflected signals from the near-well zone. The results of the second logging are compared with the first logging as shown in FIG. 4.

• • The logging process is such a process which allows logging from inside of the casing, through the casing and into the near-well zone of the layers. Such logging process in particular can be a neutron logging which determines neutron properties of the near-well zone of the layers.
  • As known the presence of hydrogen in the reflected signals corresponds to the presence of gas, while a ratio of carbon to oxygen in the reflected signals corresponds to the presence of oil.
  • As a result of the inventive method, it is possible to determine those layers which still contain oil or gas with high accuracy.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the type described above.

While the invention has been illustrated and described as embodied in a method of investigation of oil and gas producing wells, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

Claims

1. A method of determination of oil- and gas-productive layers in a well, comprising the steps of performing a first logging in a well having a casing over a potentially promising depth of a well from a space inside the casing radially outwardly through the casing by sending transmitting signals into layers near the well and receiving reflected signals, with perforations in the casing and in the layers in condition of presence of a filtrate in the layers in the near-well zone; insulating the perforations in the layers from an interior of the well; maintaining the perforations of the layers insulated from the interior of the well over a time sufficient for migration of the filtrate away from the near-well zone and accumulating in the near-well zone of the layers oil or gas; performing a second logging in condition when the near-well zone of the layers no longer contains the filtrate but can contain oil or gas; and comparing the reflected signals obtained from the second logging with the reflected signals obtained from the first logging to determine the presence or absence of oil or gas in the layers within the potentially promising depths.

2. A method as defined in claim 1, wherein said first and second logging includes using a neutron logging determining neutron properties of the near-well zone of the layers for obtaining the reflected signals in the first neutron logging and obtaining the reflected signals in the second neutron logging and comparing the signals of the second neutron logging with the signals of the first neutron logging.

3. A method as defined in claim 1, wherein said insulating includes introducing a cement solution between the casing and the layers for closing the perforations in the layers so as to interrupt a hydrodynamic communication between the layers and the well.

4. A method as defined in claim 1, wherein said maintaining includes maintaining the perforations of the layers insulated for a period of 1-3 months.