Well test interpretation of pressure recovery data after manhole acid fracturing

Wang Xibin Chen Zhihai

(Planning and Research Institute of Xinxing Oil Company, Beijing 100083)

The artificial fracture formed by acid fracturing in Well 65 is connected with the natural fracture-cave system. In view of this typical acid fracturing measure well, with the help of Saphir software developed by Kappa Company of France, the well test interpretation of the pressure recovery test data of this well is carried out by using the composite reservoir model. Some basic parameters of artificial acid fracturing and natural fracture-cave system are obtained by using nonlinear regression fitting method of typical curves and MDH characteristic straight line method, and the interpretation results are in line with the actual situation of the formation. It provides a reference research method for well test interpretation of similar acid killing wells in the future.

Acid pressure; Natural fracture-cave well test; Composite reservoir model; Pressure recovery

1 Basic situation of the reservoir

Well Sha 65 is an exploratory well about 5 kilometers northwest of Well Sha 48 in Tahe No.4 Oilfield, which is structurally located in the west wing of Aixieke No.2 structure. The open hole completion interval is 545 1.82 ~ 5520.0m, and the lithology is gray and yellow-gray microcrystalline limestone. After the drilling of this well is completed, the DST test first determines that it is a dry layer, and then acid fracturing is carried out in the test interval. From the analysis of acid fracturing construction curve, artificial acid fracturing cracks were formed in the early stage of acid fracturing, and then the pump pressure decreased, the displacement increased and the natural cracks were interconnected. The well was put into production on1September 4th, 999 12:40, and the 8mm choke produced 336 m3/d, and1September 4th, 999/10 was shut in, and the pressure test was resumed (hereinafter referred to as re-pressure).

2 Selection of explanatory parameters

The test report of well Sha 65 does not provide all the reservoir geological parameters and PVT physical parameters of fluid required for interpretation. Because this well is located in Tahe No.4 Oilfield, the reservoir characteristics and fluid properties of Sha65 and Sha48 wells are compared, and the oil and gas data acquisition results (internal data) of Tahe No.3 and No.4 in Tarim Basin, Xinjiang are 1999.

, as shown in table 1.

It can be seen from the table 1 that the crude oils of Well Sha 65 and Well Sha 48 belong to high viscosity crude oils, and the PVT properties are similar. Therefore, when interpreting the test data of well Sha 65, the oil layer thickness is the thickness of the open hole completion interval, and the comprehensive compressibility is the value of well Sha 48. See Table 2 for specific values of interpretation parameters of Well Sha 65.

Table 1 Comparison Table of Formation and Fluid Parameters of Well Sha 48 and Well Sha 65/Comparison Table of Reservoir and Fluid Parameters of Well Kloc-0/S48 and Well S65

Table 2 Well Test Interpretation Parameter Values of Well Sha 65 Table 2 S65 Interpretation Parameters

3 Interpretation of actual test data

The author uses Saphir(2.3R) well test interpretation software developed by Kappa Company in France for interpretation. In the process of interpretation, the model is identified by different means, and the interpretation model closest to the reservoir geological characteristics is selected. The same model is compared with various interpretation methods to explain reservoir parameters.

3. 1 flow history

Upon verification, the total shut-in production time of Well Sha 65 is1September 4, 1999 1438+02: 40,1September 99 10/2: 52.

Table 3 Well Test Interpretation Flowsheet of Well Sha 65 Table 3 Well S65 Flowsheet

3.2 Model identification

Figure 1 is the logging curve of pressure recovery data of well Sha 65. As can be seen from the figure, the early pressure and pressure derivative curves do not coincide (the pressure derivative curve is above 450 line, and the pressure curve is below 450 line), mainly because the wellhead shut-in surface flow is zero during the pressure recovery test, and the bottom hole flow is not caused by the wellbore afterflow effect.

Fig. 1 pressure recovery data of well sha 65 S65 double logarithmic pressure recovery diagram.

Corrected shut-in time in figure 1. In contrast, the production time of Well Sha 65 is prolonged by 0.05 hours, and the pressure recovery data is taken as the data after 143.35 hours ... The log diagram of the pressure recovery data thus corrected is shown in Figure 2.

The log-log characteristics of the pressure recovery shown in Figure 2 are as follows:

Fig. 2 The corrected log log log log log log log log log log log log log log log log log log log log log log log.

Early stage (AB): the slope of pressure and its derivative is 0.5 ~ 1.0. Because the well has undergone acid fracturing measures, it embodies the fracturing characteristics of infinite conductivity and the reservoir characteristics of double wells.

In the intermediate stage (BD), the pressure derivative appears "depression". Because the bubble point pressure of formation crude oil is about 20MPa, the original pressure of the reservoir is about 59.4MPa, there is single-phase flow in the reservoir, and the gas production is too small to be measured during well opening, so the "depression" in the pressure derivative is not caused by the escape of gas phase in the crude oil, but by the communication between the oil well and acid pressure. Therefore, the dual wellbore storage effect caused by fracture storage will cause "depression" in the pressure derivative, which can be reflected in the characteristics that the early pressure and its derivative slope are 0.5 ~ 1.0.

Late stage (EF): It reflects the radial flow characteristics of the formation. If the double-barrel reservoir effect is excluded, there are two steps on the pressure derivative curve in the middle and late stage, which shows that the fracture (artificial fracture) formed by acid fracturing measures is connected with the natural fracture-karst cave system in the formation, which can be reflected in the acid fracturing construction curve of Well Sha 65 (Figure 3), thus forming two regions with different permeability.

Fig. 3 acid fracturing construction curve of well Sha 65; acid fracturing curve of well 3 s65.

Therefore, in the actual interpretation, the main model should choose the radial composite reservoir model. Based on the above analysis, the model chosen in this paper is "infinite diversion fracture+double wellbore storage (variable wellbore storage)+radial composite reservoir+infinite boundary" when interpreting the pressure recovery data of well Sha 65.

3.3 Interpretation of formation parameters

After the above model is identified, the typical curve nonlinear regression method and characteristic straight line method of Saphir software are used for comparative interpretation, as follows:

3.3. 1 nonlinear regression method of typical curve

The model of "infinite conductivity fracture+double wellbore storage (variable wellbore storage)+radial composite reservoir+infinite boundary" is selected, and the typical curve of this model is fitted by nonlinear regression. The result is shown in Figure 4.

Fig. 4 Nonlinear regression fitting S65 logging curve of typical curve of pressure recovery data of Sha 65 well.

Through the fitting of Figure 4, the interpretation results are shown in Table 4.

Table 4 Nonlinear Regression Fitting Results of Typical Curve of Well Sha 65 Pressure Recovery Data Table 4 Reservoir Parameters Interpreted by S65 Nonlinear Regression Fitting

According to the above explanation results, we can calculate the following parameters:

(1) initial wellbore storage coefficient ci and ending wellbore storage coefficient Cf

The calculation formulas of initial wellbore storage coefficient and termination wellbore storage coefficient are as follows: