RU2394987C1 - Procedure for prevention of behind-casing flow from non perforated formation into interval of perforation - Google Patents

Abstract

FIELD: oil and gas production.

SUBSTANCE: procedure preventing flow from non perforated formation into interval of perforation consists in evaluation of ratio of absolute permeability of nearest water-bearing strata to perforated formation in interval of terrigenous Devonian, in evaluation of distance between them and in calculation of natural disconnection of collectors. If ratio of natural disconnection of collectors in the interval is less, than 2 m, probability of behind-the-casing communications is rendered as growing, and it is concluded to strengthen lining of such intervals with additional technical and process facilities. Ratio of natural disconnection of collectors is calculated from reduced mathematic expression.

EFFECT: raised reliability of behind-the-casing flow prognosis, upgraded quality of well construction.

1 ex, 1 tbl

Description

The invention relates to the oil industry and may find application in the elimination of annular flow from an unperforated formation into the perforation interval during well operation.

There is a method of developing an oil reservoir, according to which the reservoir is drilled according to the design grid. Wells are divided into categories depending on the thickness of the transition zone or impermeable layer between the oil and aquifer parts of the reservoir. They are assigned to injection or mining as intended. Wells belonging to the first category, with a thickness of the transition zone or impermeable layer up to 1.5 m, are used as injection wells. Wells of the second category with a thickness of 1.5-3 m and wells of the third category with a thickness of more than 3 m are used as production wells. The productive layer is opened in a gentle mode using drilling or hydromechanical perforators. Moreover, in part of the wells of the first category and in all wells of the second category, the aquifer part of the formation is opened by perforation under the transition zone or impermeable layer at a distance of 4-5 m from the oil-water contact. The cutter trunk installed above the reservoir. A filter with a plug is installed below the aquifer of the reservoir. Lower the pump. Pumping fluid creates depression on the reservoir. Opposite the filter of the productive part of the reservoir, a water seal is made of oil. In the transition zone and in the aquifer of the formation create a "reverse cone". The latter is an obstacle to the movement of water from the aquifer of the reservoir to the oil reservoir. Moreover, the mentioned wells of the first category are used as production wells (RF patent No. 2291287, published. 01.10.2007).

The known method eliminates the possibility of annular flow from the non-perforated reservoir into the perforation interval during well operation due to the formation of a “reverse cone”, however, the method determines a greater production of water than oil.

Closest to the proposed invention in technical essence is a method for controlling the movement of formation fluid in the annulus of a production well, which includes measuring the temperature or passive acoustic noise signal along the wellbore in different modes of its operation and identifying possible zones of annular fluid movements in which the amplitude is additionally recorded electromagnetic field in the frequency range 60-280 Hz, the presence of anomalies determine the intervals of annular flow of formation water , and in the form of anomalies - the direction of formation water movement (RF patent No. 2078923, published. 05/10/1997 - prototype).

The method allows to identify the intervals and direction of annular flows during well operation, but does not allow to predict and prevent annular flows at the stage of well construction.

The proposed invention solves the problem of predicting and preventing annular flow from an unperforated formation into the perforation interval during well operation.

The problem is solved in that in the method of preventing annular flow from the non-perforated formation to the perforation interval in the terrigenous Devonian interval, the ratios of the absolute permeabilities of the nearest aquifer to the perforated formation and the distance between them are determined, the coefficient of natural separation of the reservoirs (LRC) is calculated when the LRC is in the interval less than 2 m conclude that the probability of behind-the-casing messages increases and the need to strengthen the lining of such intervals with additional technical and technical logical measures, while the CRC is calculated by the formula:

where h is the distance between the layers, m, k _{ave. water} is the absolute permeability of the water-saturated layer, μm ² , k _ave.perf is the absolute permeability of the perforated layer, μm ² .

SUMMARY OF THE INVENTION

The quality of well construction is primarily determined by reliable separation of formations and the absence of uncontrolled flows of formation fluids behind the casing between the formations, and the influx of fluid from non-perforated formations into the well. The ability to fully develop the reservoir and achieve maximum oil recovery depends on the quality of reservoir separation. Existing technical solutions allow to identify the intervals and directionality of casing flows during well operation, but they do not allow predicting and preventing casing flows at the well construction stage. The proposed invention solves the problem of predicting and preventing annular flow from an unperforated formation into the perforation interval during well operation. The problem is solved as follows.

To prevent annular flow from the non-perforated reservoir to the perforation interval in the interval of the terrigenous Devonian, the ratios of the absolute permeabilities of the nearest aquifer to the perforated reservoir and the distance between them are determined. The coefficient of natural disunity of the reservoirs is calculated by the formula (1). KPRK has a dimension - m. When the coefficient of natural disunity of the collectors is found in the interval of less than 2 m, a conclusion is made about the increased likelihood of annular communications and the need to strengthen the lining of such intervals with additional technical and technological measures. Perform the planned activities.

The existing arsenal of fastening equipment and technology includes: mud formation, preliminary waterproofing of the formation with oil-water contact, silicate bath, guaranteed centering of the casing, installation of lip-cementing devices, turbulators, the use of high-quality cement mortar, including expanding, ensuring complete replacement of the drilling fluid with cement, etc.

The risk interval for casing messages is valid only for terrigenous Devonian wells and is not valid for the rest of the productive part of the well section. The risk of annular flow from the non-perforated formation to the perforation interval during well operation is estimated, and not the risk of the appearance of inter-reservoir flows.

Concrete example

For calculations to identify intervals with the maximum risk of behind-the-casing messages, the following parameters are required:

1. intervals of depths of collectors;

2. The absolute permeability of the reservoir.

Those. Calculation is possible only after carrying out a full complex of final logging and obtaining a final conclusion with all parameters of exposed reservoirs.

First of all, they assess the risk of annular communication of the perforated interval with the nearest reservoirs - reservoirs, as well as other oil-saturated reservoirs (future perforation intervals) with neighboring reservoirs for subsequent periods of well operation. Calculation for a specific well is carried out comprehensively to identify the intervals of possible annular communications from the lower layer up and from the upper layer down. The results are presented in table 1.

The permeability value is taken as the absolute permeability of the best interlayers in the intervals of the layers, that is, the ratio of the maximum absolute permeabilities as the most active intervals is calculated. For example, in the intervals of 1727.8-1732.0 m and 1732.0-1735.0 m, the maximum abs. permeability for the conclusion of geophysical surveys of wells.

As can be seen from the table, casing messages from the bottom up are likely in the interval 1724.8-1725.4 m (in the case of perforation of the formation in the interval 1724-1724.8 m, there is a very high probability (CRC = 0.06) of casing communication with a collector from the interval 1725.4-1726.2 m) and in a formation with a water-oil contact at a depth of 1732 m. There is a danger of behind-the-casing overflows in the interval 1726.2-1727.8 m (in case of perforation of the interval 1727.8-1732 m there is a risk annular communication (KPRK = 1.32) with the upper reservoir from the interval 1725.4-1726.2 m) and in the reservoir with a water-oil contact and a depth of 1732 m. The object is to enhance the separation of said slots available arsenal of techniques and fastening technology. In this case, to strengthen the lining, the barrel was hydromonitorized in preparation for launching the column; in addition to the column centralizers, a flow turbulator was installed at a depth of 1726.5 m, and a cuff cementing device was installed at a depth of 1732 m.

Under normal conditions (according to the prototype), such a well is 90% flooded in the first month. In the proposed embodiment, the well worked for 26 months with a water cut of produced products of 10%.

The application of the proposed method will solve the problem of predicting and preventing annular flow from an unperforated formation into the perforation interval during well operation.

Claims (1)

A method for preventing annular flow from an unperforated formation into the perforation interval, namely, in the terrigenous Devonian interval, the ratios of the absolute permeabilities of the nearest aquifer to the perforated formation and the distance between them are determined, the coefficient of natural separation of the reservoirs is calculated when the coefficient of natural isolation of the reservoirs is found in the interval of less than 2 m make a conclusion about the increased likelihood of behind-the-casing messages and the need to strengthen the support of such int vomited additional technical-technological measures, wherein the ratio of the natural dissociation of collectors is calculated by the formula:
KPRK = h / (k _ave.water / k _ave.perf ),
where h is the distance between the layers;
k _{pr water} - the absolute permeability of the water-saturated formation;
k _pr.perf - absolute permeability of the perforated formation.