Testing Research On Streaming Potential In Deep Stratum

According to literature view, water pressure inside stratum tends to reallocate with appearance of streaming potential when inject high pressure water. High-pressure water injection is widely used in secondary oil recovery, sometimes even in first oil exploitation, while high pressure polymer injection is used in third oil recovery. So if the real-time status of reservoir fluid can be monitored and calculated by the streaming potential of injection fluid, it could improve the exploitation efficiency and save exploitation cost.This thesis, firstly, introduces the research history of streaming potential, and then discusses the basic principle and application situation of streaming potential in the world. According to literature view, current researches are focus on electro-kinetic phenomena of different fluid envelope, while the streaming process of potential is still on qualitative status without technical application study on streaming potential monitor.This thesis summary the used approaches and responding principle on oil exploration at different times over three epochs, and then found that water and gas injection approach used in second generation and polymer, alkali water, microorganism, hot water and so on, injection approach used in third generation apply the same principle that the pressure caused by fluid injection accelerate the rate of fluid flow. Combing the basic principle mentioned above and literature view, thesis points out that any fluid injection to oil layer will lead to streaming potential, which means potential monitors could be used to track the streaming behavior.Oil reservoirs were divided into six groups in China, crack-controlled, fault-controlled, impervious-controlled, bedding structures controlled, Permeability rhythmic controlled, pore structure controlled. However, due to no uniformity, complexity, injection variation and water out behavior, there are lots of technical problems with oil explorations in China. Injection in reservoir heterogeneity tends to generate streaming potential, which is suit for application of streaming potential monitor approach. Inhomogeneous of fluid streaming in different layers and transition from static pressure to kinetic pressure usually lead to streaming potential, during oil exploration by water injection. Three primary factors are discussed in this thesis, which are geologic framework of oil reservoir, unusual pressures, reservoir water salinity separately. What's more, quantitative research on streaming potential monitor lays groundwork for future application.Factors relative to testing system of streaming potential monitor were discussed firstly. In order to match the testing condition to real oil layer status, this thesis lists the major litho characters, reservoir water salinity, injected fluid salinity to make sure sandstone as testing sample, distilled water and 20-32500mg/L as SPG. What's more, streaming potential testing system for oil exploration was designed in term with application background, testing aim and corresponding factors, which includes of testing bed and testing equipment.Firstly, Streaming potential testing was carried out with different injection pressure. This thesis introduces the testing procedure and then gives the detailed process of core sample handling. Berea sandstone, as testing sample, is from certain oil field of USA, and testing conditions were saturated salt with 20,200,2000,20000mg/L concentration. While, injection pressure was 0, 200,400,600,800, 1000kpa separately with constant ambient pressure 20MPa. Streaming potential coefficient of Berea sandstone with different mineralization will be available based on testing result analysis.Then, Tako sandstone from a oil field in Japan was testing in this research with testing condition oil, distilled water,200,2000mg/L saturated salt concentration,0,300,550,800, 1050Kpa increasing injection pressure and 20MPa ambient pressure. The final streaming potential coefficient was developed according to analysis on testing result. Next, this thesis compares the testing result between Berea sandstone and Tako sandstone.The results of in-door streaming potential testing with different injection pressure show the following characters:1. The increasing trend of streaming potential shows a closed relativity to increasing injection pressure.2. When injection pressure declines to 0, the streaming potential goes down to 0.3. The variation rate declines with electrical resistivity decreasing of core sample.4. Streaming potential shows litter change between the fluid injection and distilled water for same saturated core sample.5. The average value of streaming potential shows obvious relativity to pressure variation in the core sample with saturated oil.6. Distilled water injection generates lager streaming potential than oil in the core sample with saturated oil.In term with comparative analysis between medium-sandstone and grit sandstone, it believe that they present similar distinct streaming potential during fluid injection. However, all of these tastings were carried out in Japan and none one core sample is from China, so the next researches could be carried out in China with sandstone samples from different oil fields in order to collect relative statistical data, which help engineer and designer calculate the pressure distribution by streaming potential monitor.What's more, constant injection pressure testing is also carried out with thin oil,1000,6000, 32500mg/L as core-saturation fluid, distilled water as injection fluid. What's more, the injection pressure was different during several hours' injection process. This testing recorded all of the variation data both of electric resistivity and streaming potential from intact status to thorough going replacement of pore water inside core sample.The streaming potential value and coupling coefficient after stopping injection can be calculated by means of analytic data process on abundant of testing result with different test condition. The following shows the analysis result:1. The electrical resistivity increases during the pore water replacement process and the streaming potential shows the same trend under one injection pressure.2. After the pore water have been completely replaced by distilled water, the variation of electrical resistivity stopped immediately. However, the streaming potential still kept changing.Based on in-door testing results, thesis evaluates the generation mechanism of streaming potential as following:1. Electrical resistivity shows little change due to lesser permeability during the testing beginning. However, with the increasing injection pressure, the streaming potential rises obviously. When the sample is getting to be saturated, the injection pressure is up to maximum and streaming potential tends to be a constant.2. With the increasing injection volume, pore water inside sample was replaced step by step, which leads to variation of electrical resistivity. What's more, streaming potential is also increasing due to electrical resistivity.3. After the pore water inside sample has been completely replaced by injection fluid, the electrical resistivity of sample stops changing while generates a streaming potential relative to injection pressures.With the objective to validate application of streaming potential methods, out-door water injection testing was carried out in certain suburb in Japan. The depth of testing hole is 21.6m, with 0.23MPa injection pressure. Freshwater injection process lasted 16 minutes with 1441/min throughput. In this testing, streaming potential showed 1.5mv.Followings are conclusions of out-door testing:1. At the beginning of water injection, the injection area shows obvious streaming potential, and then the streaming potential declines with the increasing injection distance.2. Streaming potential is up to peak at the beginning water injection and then declines.3. Streaming potential is still existed after water injection process. It is believed the reason is that the balance procedure of underground water hasn't stopped due to the pressure head after water injection.The relationship between injection pressure, salinity of injection fluid and streaming potential was analyzed in both of in-door and out-door testing. The streaming potential coefficients with different salinity can be calculated, which lays the ground work for high precision and efficiency of oil exploration.It is proved that the variation of streaming potential of fluid inside stratum directly results from the variation of fluid pressure distribution according to masses of in-door testing results and some of out-door testing results. This relationship can be developed by data collection, data analysis and evaluation. Furthermore, the relationship between pressure and streaming potential assists us to monitor the moving condition of underground fluid. The streaming potential monitor method presents a new idea for oil exploitation technique with bright future prospects.