Shale Gas Water-based Drilling Fluid Technology Research

Shale gas is a kind of unconventional gas resources which present in the dark shale or high carbonaceous shale which are rich in organic matter, mainly exist in adsorption or the free state, the main composition is methane. Shale gas reservoir has characteristics such as self generation and self preservation, no gas-water interface, large areas of continuous accumulation, and low porosity and permeability. Shale gas resource is abundant, accounts for about 50% of the world’s unconventional gas resources. With the help of shale gas revolution, the United States not only changed the situation of natural gas consumer imports and achieved self-sufficient, lowered the domestic energy prices, but it also from a energy importer into an energy exporter. There are most abundant shale gas resources in China, but the domestic shale gas exploration and development is still in its infancy, but has been developing rapidly in recent years. Shale gas industry in China has developed rapidly in recent years, has been in China’s Bohai bay and Songliao, Sichuan and Tuha basin discovered shale of high content of organic carbon. AT present, Sinopec in Chongqing Fuling area, PetroChina in Sichuan Weiyuan area are in large-scale commercial shale gas exploitation, and achieved good results.Due to shale formation hydration expansion, coupled with complex geological of shale gas reservoir structure in our country and high incidence of downhole accident, at present our country’s shale gas well are mostly drilling with good inhibitory and lubricity oil-base drilling fluid. But owing to the high cost of oil-base drilling fluid, pollution, and the cement bond quality is difficult to guarantee, and facilities with oil-base drilling fluid are not mature. So it’s urgent need to develop a suitable for shale gas horizontal well operation of strong inhibition and high-performance water-based drilling fluid with low pollution.This paper analyzes the current situation of the development of shale gas drilling fluid at home and abroad, further studied the shale hydration expansion mechanism and restraining mechanism, compared the current commonly used shale inhibitor, selected the high concentration of calcium chloride solution as the main inhibitors, modification of xanthan gum JH-VIS as tackifier, and on this basis, developed a strong inhibitory water-based drilling fluid of high calcium.Basic formula is:the fresh water+0.5% CMC-LV (stabilizer) + 0.3 JH-VIS(flow pattern regulator)+ 2.0% FLOCAT (fluid loss agent) +2.0% SMP-1 (fluid loss agent) +2.0% RS-1 (fluid loss agent)+2.0% CMJ (fluid loss agent) + 2.5% CPI (clay stabilizer) + 20% CaCl2 (inhibitors) + 2% JLX-B (lubricant) + barite (ρ= 1.50 g/cm3).1.This system adopts the high concentration of CaCl2 solution as an inhibitor, is a kind of high calcium drilling fluid, with starch film-forming blocking agent, has good shale inhibition effect. Using shale gas drilling cuttings of Fuling to rolling recovery evaluation, first time recovery rate is as high as 97.13%, and the secondary recovery rate is 96%.2. This system use the modified organism glue JH-VIS as flow pattern regulator, and the regulator has good salt resisting property. The system has good rheological properties, and reached the requirement of low viscosity high yield value,.It can not only meet the requirement of carrying cutting capacity of horizontal well, but also has lower apparent viscosity, which is helpful to improve the rate of penetration.3. This system use several kinds of salt resistant starch compared with sulfonated phenolic resin compound as the fluid loss agent, sulfonated phenolic resin has good adsorption, can adsorb on the surface of shale, and starchy loss reduction agent has good film-forming effect, they compound with each other and make the mud filter cake thin and dense, not only has a good fluid loss effect, but also can effectively enhance the wall strength, prevent sidewall instability.4. This system adopts the polymeric alcohol JLX-B aslubricant, mud frictional resistance coefficient is 0.12, the lubrication effect is good, can satisfy the requirements on the lubrication performance of drilling horizontal well.5. This drilling fluid system has good temperature resistance, at 110℃ can still maintain good rheological property and filtration properties, there were also no significant yield value lower, and still have good ability to carry cuttings.6.This drilling fluid system has good of Density increase performance, the highest density is 1.8 g/cm3. As long as the density is less than 1.8 g/cm3, the rheological properties and filtration properties of drilling fluid can keep well, and there will be no settlement stratification and so on.7. This system has stable rheological properties, and good antifouling ability. NaCl and clay were used respectively to evaluate it’s antifouling ability, the results showed that the drilling fluid system pollution performance is good. With a small amount of NaCl or clay t polluted, it still has good rheological properties and the filtration performance.