Method for determining formation pressure and well interference

Abstract

The invention relates to methods for determining well productivity. A group of closely-spaced wells which potentially exert a mutual influence on one another is selected. The flow rates of the wells are measured, as well as the bottomhole pressure of at least one of said wells. The measurement results are recorded in a temporally synchronized manner and are converted into transient functions: a function of pressure change in each of the wells when operating at a unit flow rate, and a function of pressure change in a well when each of the adjacent wells is operating at a unit flow rate. Said transient functions are interpreted to predict formation pressure and the productivity of each of the wells. The technical result is that of making it possible to optimize well operating modes taking into account the mutual influence of wells on one another, as well as to prevent production losses arising from the need to shut in producing wells in order to measure formation pressure.

Description

[0001] METHOD FOR DETERMINING FORMATION PRESSURE AND WELL INTERACTION

[0002] The invention relates to the oil and gas production industry, in particular to methods for determining the oil productivity of wells.

[0003] An analogue is known - a method for determining the productivity of an oil reservoir in a three-dimensional interwell space - RU 2259575, 28.10.2004, including conducting ground three-dimensional seismic exploration work with 3D longitudinal waves using the common depth point (CDP) method, drilling wells with coring, electrical, radioactive, acoustic and seismic logging, well testing, and core study. Based on the combination of drilling data and well geophysical studies (WGS) using known criteria, they judge the presence of reservoirs, their capacity, permeability, hydraulic conductivity, oil productivity, water-oil contact level (WOC), location of oil fields, as well as the presence of a correlation between capacity, hydraulic conductivity and oil productivity.

[0004] The disadvantages of the analogue are the high labor intensity of the study, its long duration, high cost and low reliability of the study of the potential for increasing well production.

[0005] An analogue is known - a method for determining oil productivity with the placement of inclined and horizontal oil and gas wells based on the spectral decomposition of geophysical data - RU2314554, 09.06.2006, adopted as a prototype, including the implementation of production from a group of closely located wells that potentially have a mutual influence on each other, conducting seismic exploration of the third dimension, electrical exploration, gravity exploration and magnetic exploration work, drilling wells with core sampling, electrical, radioactive, acoustic, seismic, magnetic and gravity logging, core study, well testing and judgment based on the obtained data on the presence of oil and gas objects, wherein the traces of seismic time cubes, electrical exploration data, magnetic exploration and gravity exploration, curves of geophysical studies of wells in the target interval are transformed by spectral decomposition into multichannel spectral-time columns,each of which becomes a multichannel unit of geophysical information displaying the properties of the geological environment, determine multidimensional mutual correlation dependencies between spectral-time columns both within each geophysical method and between methods, form a single information array linked to drilling data, based on the integrated use of artificial neural networks, statistical and spectral-correlation algorithms, transform this array into a filtration-capacitive, oil and gas productive three-dimensional geological models in the form of cubes of specific capacity and hydraulic conductivity of reservoirs, coefficients of their oil and gas productivity,taking into account the levels of water-oil-gas contacts and the structural-tectonic factor, oil and gas objects are identified and, based on the maximum values ​​of the filtration-capacity properties of reservoirs and their oil and gas productivity, the location of wells on the ground and the tracing of inclined and horizontal wellbores in three-dimensional space are determined.

[0006] The disadvantage of the analogue is the low efficiency of determining oil productivity, due to the lack of consideration of the mutual influence of wells from a group of closely located wells on each other.

[0007] An analogue is known - a method for determining reservoir pressure - RU2239700, 20.08.2002, selected as a prototype, including stopping a well operating in a stationary mode with known characteristics, recording the pressure increase in it and processing the resulting pressure recovery curve (PRC). The disadvantage of the analogue is the loss of production associated with the need to stop well production for a long period. In addition, the method is inaccurate if the well is under the influence of intense interference with surrounding wells.

[0008] The technical result of the proposed invention consists in increasing oil production by optimizing the operating modes of wells in the studied area, by more accurately determining reservoir pressure than in analogs, taking into account the mutual influence of wells on each other, and also by eliminating production losses associated with the need to stop production wells to measure reservoir pressure.

[0009] The technical result is achieved in a method for determining reservoir pressure and well interaction using a multi-well retrospective test (MWRT), in which pressure in a well is measured, a group of closely spaced wells that potentially have mutual interaction are selected, the flow rates of these wells and the bottomhole pressure in at least one well are measured with recording of measurements synchronized in time, the obtained measurement data are converted into transition functions: the function of the change in pressure of each of the specified wells during its operation with a single flow rate - the diagonal transition characteristic of the well, and the function of the change in pressure in the well during the operation of each of the adjacent wells with a single flow rate - the cross-well transition characteristic of each interval between the wells, interpreting the specified transition functions, a forecast of the reservoir pressure and productivity of each of the specified wells is made.

[0010] Fig. 1 shows a 2D structural map with the location of the studied group of wells: OP-1, OP-2, OP-3, OP-4, WI-5.

[0011] Fig. 2 shows a 3D cube of initial oil saturation with well locations. Fig. 3 shows graphs of changes in bottomhole pressure for well OR-1 and flow rates for all wells in the group over time (abscissa axis), illustrating the production history.

[0012] Fig. 4 shows a graph of the transient response and its logarithmic derivative for well OR-1, with pressure on the ordinate axis and time on the abscissa axis.

[0013] Fig. 5 shows a graph of the cross-well transient response and its logarithmic derivative for interwell intervals, with pressure on the ordinate axis and time on the abscissa axis.

[0014] Fig. 6 shows a graph of the quantitative mutual influence of wells, with pressure on the ordinate axis and time on the abscissa axis. The lines represent the quantitative contribution of each well to the change in pressure in the drainage area of ​​the central well of the study.

[0015] Fig. 7 shows graphs illustrating the assessment of the reliability of the study using a comparison of actual and calculated data in the validation interval not used in the analysis of MRI data.

[0016] Fig. 8 shows the graphs of the well flow rate forecast. Time is plotted along the X axis, pressure and flow rate are plotted along the Y axis. The time period before the vertical dotted line is historical data, after it is forecast data.

[0017] Let us consider an example of implementation of the method for determining reservoir pressure and well interaction using the multiwell retrospective test (MWRT) method. First, a group of closely spaced wells is selected that potentially have mutual influence on each other. The example under consideration describes a real field, where a group of five closely spaced wells is located on the site, which are designated: OP-1, OP-2, OP-3, OP-4, WI-5. The position of the wells under study is shown in Fig. 1. The cube of initial oil saturation of the synthetic field model is shown in Fig. 2.

[0018] The flow rates of these wells and the pressures in them are measured, with measurements recorded with time synchronization. The measurements are made by sensors measuring the current flow rate and current pressure, respectively, located in each well. The operation history of these wells is shown in Fig. 3.

[0019] Next, the multiwell retrospective test (MRT) method is used. Data processing and the multiwell deconvolution process are performed in the MRT processing software tool. The obtained measurement data are transformed into transition functions: the function of pressure change for each of the specified wells when it operates with a single flow rate - the diagonal transition characteristic (DTC) of the well and the function of pressure change in the well when each of the neighboring wells operates with a single flow rate - the cross-well transition characteristic (CWTC) of each interval between the wells. For this purpose, the data from the specified sensors are preliminarily smoothed using a wavelet filtering algorithm with a threshold value, and then filtered to 1 point per minute using the wavelet filtering threshold value algorithm, which leads to a significant reduction in noise and facilitates further data processing.

[0020] Then, the multiwell deconvolution procedure (MWD) is performed on the preprocessed data, which results in the well diagonal transient response and cross-well transient responses for each interval between wells, which represent the pressure response to operation with a single flow rate of the adjacent well. The MWD procedure identifies the pressure response to the well's own flow rate (Fig. 4) and the flow rate of each of the surrounding wells (Fig. 5). In this case, the DWC takes into account the formation hydraulic conductivity, the well skin factor, and the drainage area dimensions, while the CWC takes into account the interwell hydraulic conductivity.

[0021] By comparing the well performance history with the well operation history, we obtain functions that determine the mutual influence of the wells on each other, the graphs of which are shown in Fig. 6. The graphs in Fig. 6 represent the quantitative contribution of each well to the pressure change in the drainage area of ​​the central well of the study. As the well flow rate increases, its contribution to the pressure change increases, and as it decreases, it decreases. To determine the quantitative contribution of each well to the pressure change in the drainage area of ​​the central well of the study, the initial value of the reservoir pressure is normalized relative to zero at the time when the wells were not operating. Then the wells are started up, and they begin to influence the reservoir pressure value in one way or another. Injection wells (WI-5) increase the pressure in the area of ​​the central well of the study OP-1, and production wells (OP-2, OP-3, OP-4) decrease the pressure in the area of ​​the central well of the study.The magnitude of such a contribution to the change in pressure from each well is shown in Fig. 6. If we sum up all the graphs, we obtain a graph of the change in reservoir pressure in the area of ​​well OR-1.

[0022] Thus, using the MDKV approach, transient characteristics normalized to a single flow rate are obtained. The reliability of the solution is verified using blind cross-validation (Fig. 7).

[0023] By interpreting the specified transition functions of the DPH and KPH using the approaches used in interpreting well hydrodynamic studies, a forecast of the reservoir pressure and productivity of each of the specified wells is made. At this stage, based on the functions of the mutual influence of the wells on each other (Fig. 6), a forecast (Fig. 8) is made for the well flow rate for each well operation scenario. For this, such conditions are selected that the model curve 1 (Fig. 8) coincides with the transition characteristic. A series of forecasts are prepared for various well operation modes and for implementation, a well operation mode in the group is selected such that the estimated oil production is maximum. In the graph of Fig. 8, this mode corresponds to the model curve shown by the dash-dotted line 1. That is, with the flow rate change scenario for the group of wells specified in the example, the pressure will drop as shown in the graph by the dash-dotted line.Further production is carried out in accordance with the obtained forecast based on the criterion of maximum productivity of all wells in the specified group.

[0024] The proposed method for determining reservoir pressure and well interaction using the multi-well retrospective test method provides a higher quality production forecast based on the criterion of maximum productivity of all wells in a group due to the following differences from analogues.

[0025] Classical approaches to forecasting using pressure recovery curves (PRC) and level recovery curves (LRC) do not provide for unambiguous quantitative interpretation with intensive influence of neighboring wells, since the shape of diagnostic pressure graphs is strongly distorted by the influence of the environment. Single-well deconvolution, used in the analogue of the proposed method, does not allow overcoming this difficulty, since the result is strongly influenced by the intensity of interaction with neighboring wells.

[0026] The MRI data analysis used in the proposed method, the core of which is the multi-well deconvolution technology, due to the algorithm for taking into account the influence of the surrounding wells on the pressure field, works more reliably compared to a single-well method, allowing one to determine the hydraulic conductivity of the formation, since the well-by-well transient characteristic is cleared of the influence of interference and allows one to identify the radial flow regime on the diagnostic pressure graph.

Claims

Invention formula A method for determining reservoir pressure and well interaction using a multi-well retrospective test (MWRT) method, in which pressure in a well is measured, characterized in that a group of closely spaced wells that potentially have mutual influence on each other are selected, the flow rates of these wells and the bottomhole pressure in at least one well are measured with recording of measurements synchronized in time, the obtained measurement data are converted into transition functions: the function of the change in pressure of each of the said wells during its operation with a single flow rate - the diagonal transition characteristic of the well, and the function of the change in pressure in the well during the operation of each of the neighboring wells with a single flow rate - the cross-well transition characteristic of each interval between the wells, interpreting the said transition functions, a forecast of the reservoir pressure and productivity of each of the said wells is made.

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