SU1756549A1 - Open0hole testing method - Google Patents

Abstract

Uses: Field of testing open wells during exploration for oil and gas. SUMMARY OF THE INVENTION: In the process of drilling after testing a formation in an open hole, the allowable pressure drop is determined depending on the physicomechanical properties of the clay rocks that are in contact with the reservoir.

Description

cl

WITH

This invention relates to open hole testing during oil and gas exploration.

The known method of testing wells with a reservoir tester, in which a call for fluid inflow is performed at an elevated depression, and further during sampling, the depressions in the reservoir are reduced to the value at which the bottomhole pressure exceeds the saturation pressure.

The disadvantage of this method is the neglect of the physico-geological and mechanical properties of the rocks composing the boundary zone.

The closest to the present invention is a method in which a permissible depression to a formation is recommended because of the prevention of reducing the permeability of the bottomhole zone due to the effectiveness of stresses in the reservoir rock to critical values causing plastic deformation of the rock.

The disadvantage of this method is that it does not take into account the discharge of the formation from the rock pressure while reducing the back pressure on the formation when it is tested in the drilling process.

The aim of the invention is to increase the reliability of well testing by maintaining the permeability of the wellbore zone of the test formation.

The goal is achieved by the fact that the maximum allowable depression in the process of testing is chosen from the condition of limiting the depth of penetration of the mud into the bottom zone of the reservoir in its most unloaded part (in the roof or sole).

After deepening the well to a depth determined by geological engineering, a complex of geophysical studies is carried out. According to GIS choose

vi

sl o cl

Ј o

reservoir, which must be tested in the open shaft. The parameter of the reservoir properties Ops Le is determined (where Ohc is the relative PS anomaly, pe is the effective formation thickness). Knowing the value of this parameter, the potential productivity of the test formation is determined from the potential productivity versus reservoir properties parameter, built on the basis of test formations that are in similar geological conditions of a given oil and gas field. At the same time, the productivity, calculated from the hydroconductivity of a remote zone, is taken as potential productivity. The last parameter is determined by processing the pressure recovery curve.

The electrical resistivity is determined from the induction log of clay rocks in contact with the reservoir. Knowing this value, the adhesion coefficient is determined from the curve of the adhesion coefficient of the clay rock from the electrical resistivity. The dependence of the clay adhesion coefficient on the electrical resistivity is found using experimental work with core material or from field experimental work on wells.

In the formation test, the pressure drop is controlled on the basis that the pressure drop does not exceed the following value;

L P Pg - Pz + 2.39 K,

where Pr is the pressure of the hydrostatic liquid column in the wellbore, MPa;

Рз - bottomhole pressure during the subsequent well drilling after testing, MPa;

K - coefficient of adhesion of clay rocks in contact with the reservoir, MPa.

Based on open-hole well test data, the actual productivity coefficient is determined and compared with the potential productivity factor.

The invention is illustrated as follows. At a well depth of 2500 m, a complex of geophysical surveys was carried out. According to GIS, a reservoir was identified in the range of 2420 - 2424 with an effective thickness of 4 m and a relative anomaly “ps 0.7. According to the dependence of the coefficient of potential productivity ijn on the parameter of reservoir properties One ha 2.8 m, the coefficient of potential productivity for a given stratum tjn is determined - 10 m / day-MPa. The dependency was

built according to test data from layers in similar mining and geological conditions.

According to the diagram of the induction method, the electrical resistivity of clay rocks that are in contact with the reservoir is 6 Ω-m. From the curve of the adhesion coefficient versus the electrical resistivity of the clay, K 5 MPa was determined.

This dependence is based on experimental work with core material.

The pressure of the hydrostatic liquid column, provided that the well is filled to the full depth, Pr 24.2 MPa. Downhole pressure while drilling against productive formation P3 is 27.8 MPa.

With the original data given above, the maximum allowable pressure drop

А Р Рг - Рз + 2,39хК - 8,4 MPa. When testing a well with the aid of a formation tester descending on drill pipes, the maximum difference was 8 MPa.

The actual productivity coefficient measured during testing of a well in a column is equal to 8.8 m3 / day MPa, which is 88% of the potential productivity.

Claims (1)

The invention The method of researching wells in the open hole, including conducting geophysical surveys of wells, calling the flow of fluid or gas from the reservoir, the establishment of the allowable pressure drop, characterized in that, in order to increase the reliability of well testing by maintaining the permeability the bottomhole zone of the test formation, the friction coefficient of the clay in contact with the formation is determined, and the maximum allowable pressure drop is determined from the expression; A P Pg - Re + 2.39 K. where Pr is the pressure of the hydrostatic liquid column in the wellbore, MPa; РЗ - bottomhole pressure during the subsequent well drilling after the test, 5 MPa; K - coefficient of adhesion of the clay rock contacting with the test layer, MPa.