The geological structure of Shengli oil region is complex, and the well test curve reflecting its dynamic characteristics is also extremely complex. On the basis of comprehensive analysis of well test data of electronic manometer since Shengli oil region 15, the curve characteristics of different well test data are studied, including the characteristics of variable wellbore storage curve and data interpretation method. Curve characteristics and data interpretation methods of different reservoir outer boundaries; And the problems and solutions in multi-layer and multi-well well test in Shengli Oilfield. On this basis, a set of well testing methods and data interpretation methods suitable for the complex geological characteristics of Shengli Oilfield are summarized.
Well testing; Well test interpretation; Shengli oil region of multi-layer reservoir with internal and external boundaries
I. Introduction
Modern well testing in Shengli Oilfield started at 1985. After fifteen years of introduction, development and application research, a series of modern well testing technologies have been formed, including surface direct reading test, bottom hole storage test, offshore sliding test and pumping well annular test. Pressure and temperature test, pressure recovery test, pressure drop test, interference test, pulse test test, system test, improved isochronal test, edge exploration test, horizontal well test, pumping well annular test, fracturing, acidizing, water plugging evaluation test and thermal recovery reservoir parameter calculation have been carried out successively. Up to now, 280 wells (layers) have been tested by electronic manometer, which provides important dynamic data for oilfield exploration and development. However, due to the complex geological structure and various reservoir types in Shengli Oilfield, the well test curve reflecting reservoir characteristics is also extremely complicated, and it is very difficult to interpret well test data. In order to improve the level of well test interpretation and increase the application value of well test data, these data should be comprehensively analyzed and applied in combination with the research results in the process of oil and gas reservoir development, so as to promote the continuous development and progress of well test technology in our bureau. On the basis of comprehensive analysis of well test data of electronic manometer in Shengli Oilfield, the well test data of different types of reservoir inner boundary, reservoir outer boundary, multi-layer reservoir (including layered test) and multi-well test are studied and analyzed.
Secondly, the well test data of different internal boundary types are analyzed and studied.
The inner boundary model is determined by wellbore conditions, including wellbore performance and completion. Wellbore dynamics refers to physical phenomena related to wellbore dynamic effects, including wellbore storage effect, wellbore phase change effect, wellbore temperature effect, wellbore leakage and so on. Completion refers to the influence related to the wellbore itself and the physical structure of the formation near the borehole wall, including wellbore pollution, perforation, oil layer penetration thickness, whether there are cracks and well deviation, etc. These conditions have great influence on unstable well testing, and often directly affect the accuracy of interpretation results.
1. Line source well
Regardless of wellbore performance and completion, the radius of wellbore is very small compared with the size of reservoir, and the radius of well is approximately regarded as zero. At this point, the well is called line source well. When the borehole radius is zero, the solution of the interpretation model is called line source solution.
The line source well model is widely used in the interpretation of interference test data, and is generally selected when the internal boundary of the excitation well cannot be determined.
Essay on exploration and development in Shengli oil region
Where: PD-dimensionless pressure;
S-skin coefficient;
CD—— dimensionless wellbore storage coefficient;
PD-dimensionless change of wellbore storage pressure;
L(PD)- ideal reservoir model (S=0, c). = 0) in Laplace space;
Z- laplace variable.
The variable wellbore storage pressure function given by Fair is an exponential function:
Where: cφd- constant;
Essay on exploration and development in Shengli oil region
TD- dimensionless time.
Formula (2) is transformed into formula (1) by Laplace transform, and then inverted to real space, that is, the typical curve of variable wellbore storage in exponential form is obtained (Figure 1 and Figure 2). In the early stage, wells with variable wellbore storage will show similar characteristics to those with constant wellbore storage and a storage coefficient of CφD, followed by a transition period in which the wellbore storage is variable, and then in the later stage, wells will once again show the same wellbore storage controlled only by CD.
In some cases, a wellbore storage pressure function that changes more dramatically than the exponential form is needed. Haggman gave another form of variable wellbore storage function-error function:
Essay on exploration and development in Shengli oil region
Where: α d-dimensionless wellbore storage time;
Error function.
The transition section of variable borehole storage curve with error function is larger and stronger. Using multiple variable wellbore storage pressure functions PφD 1, pφ D2 ..., a complex variable wellbore storage model can be generated. For example, the early wellbore storage decreases, and then the wellbore storage increases. For some gas wells with liquid in the wellbore, this wellbore storage feature sometimes appears in the pressure build-up test. In the early days, the compressibility of natural gas decreased continuously, which led to the decrease of wellbore storage. Later, with the liquid falling back and phase redistribution, the wellbore storage coefficient increased.
Figure 1 Typical curve of wellbore storage increase
During the interpretation of test data of 280 wells in Shengli Oilfield, there are many phenomena of wellbore storage changes. The well test data of * * * 105 has variable wellbore storage effect, including the curve that the wellbore storage coefficient first increases, then decreases and then increases. For example, the 73rd and 74th layers of Dongying Formation were tested in Chengbei Gu4 well from July 3rd, 1999 to June 5th, 1999 at/kloc-0. Before the well shut-in, the oil production was 3 13m3/d and the gas production was 26571m3/d. After the well shut-in, part of the natural gas re-dissolved into the oil, resulting in a decrease in wellbore storage. Through fitting, the final wellbore storage coefficient is 1.08× 10-2m3/MPa, the ratio of initial and final wellbore storage coefficient is 9.924 17m3/MPa, and the dimensionless wellbore storage time is 7400.
Changing borehole storage has an adverse effect on data interpretation, especially when the changing borehole is stored for a long time and there is an outer boundary near the well, which often covers up the initial outer boundary reflection, such as Fu11-8 well, thus affecting the interpretation of parameters such as the outer boundary. At present, this adverse effect can not be effectively solved in well test interpretation theory, but it can be solved by improving test technology. The specific method is to shut in the well through the bottom hole shut-in device or measure the change of bottom hole production with a bottom hole flowmeter to eliminate the influence of wellbore storage change on well test data.
Fig. 2 Typical curve of wellbore storage reduction
3. Skin coefficient
In the process of oilfield exploration and development, the skin factor determined by unstable well testing method is widely used in reservoir damage evaluation. However, the skin factor obtained by well testing is a total skin factor, which includes not only the real skin factor caused by the pollution and blockage of oil and gas reservoirs near the bottom of the well by drilling fluid and completion fluid, but also the sum of the pseudo skin factors caused by imperfect well opening, well deviation and non-Darcy flow.
The curve characteristics of this reservoir model are shown in Figure 4, which mainly shows four flow periods.
The early stage (curve A) is the part affected by wellbore storage.
Hourly interval (curve B): The fluid only flows into the wellbore from the high permeability layer, similar to the multi-layer reservoir without cross-flow, and the pressure derivative curve is horizontal on the log-log diagram.
Transition period (curve C): the low permeability layer starts to produce, interlayer channeling occurs, and the production curve and pressure curve tend to change gently.
Late stage (large time period, curve D): When the time is large enough, the production of the two layers reaches balance, the fluid flow is similar to that of a single-layer reservoir, and the pressure derivative curve reflects the radial straight line segment of the total system.
3. Example analysis
In the well test data of multi-layer reservoirs in Shengli Oilfield, most of them show the characteristics of homogeneous reservoirs, that is, the properties of each layer are similar, but some wells show obvious multi-layer characteristics, such as Gudong 10- 13 and Shenghai 8. For these wells, it is generally difficult to obtain the parameters of each sub-layer by using the above two models, and the solution is to adopt layered testing. Here, taking Gudong 10- 13 well as an example, this method is briefly introduced. Well Gudong 10- 13 has three production intervals. On September 8, 2009 1999, the storage electronic pressure gauge and intelligent delayer were lowered into the bottom hole, and the well was opened and closed layer by layer according to the pre-programmed program, and the bottom hole pressure change was automatically recorded. In the test of this well, the third layer (the first layer and the second layer) was opened for 5 days, and then the third layer was closed for measurement. The liquid volume, oil volume and water content of the first three layers are 16.6m3/d, 0.7m3/d and 96.6% respectively. In layered test, the water production of the first and third layers is 100%. Although the thickness of the second layer is only 2.0m, the oil production is as high as 34.2m3/d. It is explained that the permeability of the first and third layers are11×/kloc-0 and 0-3 μ m2 respectively. The skin factor is 44.4, and the permeability and skin factor of the second layer are 574.88× 10-3μm2 and -0. 15, respectively, indicating that the second layer has good reservoir characteristics. According to the measured pressure, the static pressures of the first, second and third layers are 13.203 1, 14.9668, 19.5335MPa, and the pressure coefficients are 0.97, 0.94 and 1.00, respectively.
V. Multi-well test
The purpose of multi-well testing is to determine the connectivity between wells and solve the stratigraphic characteristics between wells. Interference well testing is the most commonly used and mature multi-well well testing method. During well testing, one well is used as an excitation well, and another well or wells are used as observation wells. One well can also be used as an observation well, and another well or wells can be used as stimulation wells. The stimulation well changes the working system, which leads to the formation pressure change (often called "interference signal"); Run a high-precision pressure measuring instrument into the observation well to record the pressure change caused by the change of the working system of the excitation well. From whether the observation well can receive the "interference" pressure change, it can be judged whether the observation well and the excitation well are connected, and from the time and law of the received pressure change, the flow parameters between wells can be calculated.
The interference well test of Gao 17 fault block is taken as an example for analysis. Gao 17 fault block is the main oil-bearing fault block in Gaoqing oilfield. Since the water injection development of this fault block in June199065438+1October1October, other wells have no obvious impact except Gao 17-22. Analyze the reasons. In order to verify the sealing of the fault and the connectivity of oil and water wells, and adjust the injection-production structure, the interference well test was carried out on this fault block.
Fig. 5 Measured Linear Diagram of Well Gao 17-9
Well Gao 17-9 is selected as the observation well and well Gao 17-5 1 (water injection well) is selected as the stimulation well in this experiment. The test started at 199 1 year 1 month 1 day and ended at 199 1 year1day. During this period, the injection was stopped twice and started 1 time. Fig. 5 is a linear graph of this test.
Well Gao 17-9 was washed before well testing. As the liquid level drops, the pressure drops, as shown in Figure 5. At the beginning of the test, Gao 17-5 1 well has been flooded. After the injection was stopped for 20.38 hours, the pressure in the observation well continued to decrease, and then the pressure naturally resumed to increase. After the injection was stopped for 40 hours, the stimulation well began to inject with an injection rate of 302m3/d, and the injection was stopped after 96 hours. During this period, the observed well pressure still increased by 0.044MPa according to the original trend, and it was observed for 7 1.86 hours after the injection was stopped, but the pressure still increased, with no downward trend. During the whole testing process, the pressure recovered to 0.093MPa. As can be seen from the curve, the pressure recovery of Well Gao 17-9 was not affected by several excitations of Well Gao 17-5 1. The reason is that there is a fault in the east of the fault block, which leads to the disconnection of two wells, thus confirming that the fault has good sealing property.
Conclusion of intransitive verbs
Wellbore storage has a negative impact on data interpretation, and its impact should be reduced as much as possible through the improvement of construction technology; The skin factor obtained by pressure recovery or pressure drop well test often cannot represent the pollution degree of reservoir. Skin factor should be decomposed according to well opening and well deviation to determine the real pollution of reservoir.
Using well test method to determine the outer boundary of reservoir has high accuracy, so all wells that meet the well test conditions should be tested. Because well test interpretation has multiple solutions, we should refer to other geological data as much as possible when interpreting the boundary.
Well test data of multi-layer reservoirs is still a difficult point in well test interpretation at present. If the parameters of each sub-layer need to be obtained, it is necessary to carry out layered testing, but the disadvantages of layered testing are heavy workload in field construction and harsh testing conditions.
Main references
[1] Lin Chia en. Practical well test analysis method. Beijing: Petroleum Industry Press, 1996.
Don, Liu Huaqiang. Well test analysis of variable wellbore storage. Natural gas exploration and development,1997,20 (4).
[3] I'm Vasquez and I'm Camacho velazquez. Short-term well test analysis affected by wellbore storage change. 1998。
Li kexiang Drilling and completion technology for protecting oil and gas reservoirs. Beijing: Petroleum Industry Press, 1993.