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Several ultra-low permeability drilling fluid performance testing methods

2022-06-14

The filtration loss of drilling fluid is an important indicator of drilling fluid performance. For decades, filter paper has been used as an isolation medium for testing drilling fluid filtration, but the pores of filter paper are homogeneous, while the pores of the formation are heterogeneous, so they cannot accurately reflect the actual situation of the formation. Using the sand bed and core with heterogeneous pores to measure the fluid loss of drilling fluid or the depth of filtrate entering the core can more truly reflect the fluid loss of drilling fluid downhole. The quality of the mud cake is another important indicator reflecting the performance of the drilling fluid. During the research and use of the drilling fluid, especially when drilling into the permeable and fractured formations, the quality of the mud cake affects the plugging performance of the formation and the stability of the wellbore. performance and reservoir damage have important implications. The mud cake of drilling fluid is divided into outer mud cake and inner mud cake. The mud cake outside the well wall is the outer mud cake, and the mud cake inside the well wall is the inner mud cake. In the process of laboratory research and field application, more attention is paid to the quality of the outer mud cake of the drilling fluid. In fact, the outer mud cake of the drilling fluid is often damaged by the flow rate, displacement of the drilling fluid, and the activities of the drill bit and the drilling tool, while the inner mud cake is often damaged. It is not affected by these factors. Therefore, the quality of the inner mud cake can better reflect the drilling by measuring the filtration loss of clean water on the core after stripping the outer mud cake or the depth of the filtrate entering the core and the change of the core pressure-bearing capacity. Fluid loss in downhole and its effect on formation plugging performance, wellbore stability and reservoir damage.

 

Several ultra-low permeability drilling fluid performance testing methods

 

l. Sand bed fluid loss test method

 

1.1 Visual medium pressure sand bed filtrate reducer and test method

 

1) Visual medium pressure sand bed filtrate reducer. Its structure is shown in Figure 1. It is similar to the API fluid loss meter ZNS-5A produced in Qingdao. The drilling fluid tank is replaced with a wall thickness of 6mm, a length of 500cm, and a cross-sectional area of ??18cm. The transparent plexiglass cylinder, the external equipment is the same as the medium pressure fluid loss meter ZNS-5A (API).

 

2) Test method for medium pressure sand bed filtration reduction. Add 350cm to the cylinder. Sand with a particle size of 0.45-0.90mm, washed with clean water and dried, compacted and flattened, slowly added 500mL of drilling fluid, and tested the filtration loss for 7.5min or Measure the depth of the filtrate into the sand bed. Table 1 shows the polymer drilling fluid prepared in house and the drilling fluid at a depth of 1100m in Wells 1-64 of Dagang Oilfield after adding zero filtration loss wellbore stabilizer and converting it into ultra-low permeability drilling fluid before and after API filtration loss and medium pressure sand bed filtration diagrams 1 The test results of the loss of the visual medium pressure sand bed filtrate reducer. It can be seen from Table 1 that there is no corresponding relationship between the fluid loss of the medium pressure sand bed and the API fluid loss, and the fluid loss of the medium pressure sand bed is not a function of the square root of time. The zero-fluid-loss wellbore stabilizer has good plugging ability for sand beds with different porosity. The results of the medium-pressure sand bed filtration reduction test can more accurately reflect the filtration loss of the drilling fluid downhole.

 

1.2 High-temperature and high-pressure sand bed filtrate reducer and test method GGS71-A high-temperature and high-pressure filtrate meter was used, the filter paper was cancelled, and 200g (particle size 0.45-0.90mm, 40-60 mesh or 60-80 g) was directly added. Item) washed and dried sand, added 300 mL of drilling fluid to carry out conventional high temperature and high pressure fluid loss test, Table 2 is the polymer drilling fluid prepared indoors and the drilling fluid at a depth of 1100m in Wells 1-64 of Dagang Oilfield, adding zero fluid loss to the wellbore to stabilize The test results of high temperature and high pressure fluid loss and high temperature and high pressure sand bed fluid loss before and after the agent is converted into ultra-low permeability drilling fluid. It can be seen from Table 2 that the high temperature and high pressure filter loss of the sand bed is not a function of the square root of time, and has no corresponding relationship with the high temperature and high pressure filter loss. The zero-fluid-loss wellbore stabilizer has good plugging ability for sand beds with different pores under high temperature conditions, and can achieve near-zero fluid loss.

 

Several ultra-low permeability drilling fluid performance testing methods

 

2. Test method for plugging crack performance

 

In the prepared base slurry, various proportions of zero-filtration wellbore stabilizers were added, and the D2M-01 plugging device was installed, and according to its operating procedures, the drilling fluid was used to plug fractures at different temperatures. The test results are shown in Table 3. It can be seen from Table 3 that the addition of 1.5 zero-fluidization wellbore stabilizer can seal fractures with a fracture width of less than 1 mm, and the temperature resistance can reach 150. C. For cracks with a width of more than 2mm, using an appropriate amount of zero-fluidity wellbore stabilizer and an appropriate amount of bridging particles such as walnut shells with appropriate particle size can achieve the effect of plugging the leakage, and the temperature resistance can reach 150. C, only using walnut shell can not achieve the effect of plugging.

 

Several ultra-low permeability drilling fluid performance testing methods

 

3 Evaluation method of core filtration loss reduction

 

3.1 Core filter loss evaluation instrument] The high temperature and high pressure core filter loss meter (as shown in Figure 2) is modified from a static core flow tester, and the core holder is replaced by a high temperature and high pressure core holder, and drilling fluid is added. Cooling and receiving device.

 

3.2 Core filtration test method

 

Put the core into the high temperature and high pressure core holder, heat it to the required temperature, add the prepared drilling fluid into the drilling fluid cup, open the condenser, pressurize it to 0.7MPa with the hand pump, open the advection pump to pressurize To 4.2MPa, measure the volume of the filtrate in the liquid cup after 30min. If table 3 zero fluid loss wellbore stabilizer plugging fracture test results at different temperatures Note: base slurry is 4.0 bentonite + o. 5FA367+0.8NPAN+0.3XY27+1.0FT1+0.3CSW1+15.00o barite. There is no filtrate in the liquid cup of the high-temperature and high-pressure core filter loss meter. After the high-temperature and high-pressure core holder is cooled, remove the core and measure the depth of the filtrate entering the core. Table 4 shows the results of the high temperature and high pressure core filtration test results before and after the polymer drilling fluid prepared in the laboratory and the field drilling fluid at a depth of 1100 m in Wells 1-64 of Dagang Oilfield before and after adding zero-fluid-loss wellbore stabilizer to ultra-low permeability drilling fluid.

 

It can be seen from Table 4 that the core high temperature and high pressure filtration loss has no corresponding relationship with the filter paper API filtration loss and the high temperature and high pressure filtration loss, but it is consistent with the trend of the change law of the filtration loss on the sand bed, that is, the sand bed filtration loss and The high temperature and high pressure fluid loss on the sand bed is consistent with the trend of the change law of the high temperature and high pressure fluid loss on the core. The zero-fluid-loss wellbore stabilizer has a good plugging ability to the core under high temperature conditions, and can effectively reduce the depth of drilling fluid entering the core, and can even achieve near-zero fluid loss.

 

4. Evaluation method of core bearing capacity

 

In the high-temperature and high-pressure core filtrate reducer, put the 5cm long core into the high-temperature and high-pressure core holder, add the prepared drilling fluid into the drilling fluid cup, pressurize it to 0.7MPa with the hand pump, and open the advection flow. The pump was pressurized to 4.2MPa, and after 30min, the amount of filtrate in the liquid cup was measured. If there is no filtrate in the cup, remove the core and measure the depth of the filtrate into the core. Remove the core that has been filtered out of the test core, gently scrape off the filter cake on the surface of the core, put it back into the core holder, replace the drilling fluid in the drilling fluid cup with clean water, pressurize, turn on the advection pump, and gradually Pressurize until there are droplets in the filtrate receiving cup. At this time, the pressure of the advection pump is the pressure bearing capacity of the core. Table 5 is the test results of the core filtration before and after adding the zero filtration wellbore stabilizer to the polymer drilling fluid prepared in house, and the maximum pressure test results before and after scraping the filter cake on the core surface measured when the flow rate of clean water is 1.0 mI/min. It can be seen from Table 5 that the type and performance of drilling fluid have an important influence on the core pressure-bearing capacity, and the strength of the inner mud cake formed by different types of drilling fluid is different. The zero-filtration wellbore stabilizer can not only reduce the filtration loss of drilling fluid cores, but also enhance the strength of the mud cake in the cores and greatly improve the pressure-bearing capacity of the cores.

 

Several ultra-low permeability drilling fluid performance testing methods

 

Several ultra-low permeability drilling fluid performance testing methods

 

5 Conclusion

 

1) Using a heterogeneous sand bed and core to measure the filtrate of drilling fluid or the depth of filtrate entering the core can more truly reflect the filtrate of drilling fluid downhole. 2) The test of drilling fluid API fluid loss and sand bed fluid loss shows that the sand bed fluid loss is not a function of the square root of time, and there is no corresponding relationship between the sand bed fluid loss and the API fluid loss. 3) The high temperature and high pressure fluid loss on the sand bed and the high temperature sand bed is consistent with the trend of the change rule of the high temperature and high pressure fluid loss on the core. 4) The quality of the inner mud cake can better reflect the effect of drilling fluid on the formation by measuring the filtration loss of clear water on the core under high pressure or the depth of the filtrate entering the core and the pressure bearing capacity of the core after the outer mud cake is peeled off. The effect of plugging performance, wellbore stability and reservoir damage. 5) Zero filtration hole stabilizer can not only reduce the filtration loss of drilling fluid on the sand bed and core, but also enhance the strength of the mud cake in the core and greatly improve the pressure-bearing capacity of the core, thereby expanding the safe density of drilling fluid purpose of the window.