Research And Application Of High Performance Water-based Drilling Fluid In Mahu Well Area

The formation of Mahu block in Xinjiang oil field has strong heterogeneity,high clay mineral content,and is prone to hydration expansion and hydration dispersion.Moreover,the formation leakage is serious,and the plugging material used on site does not match the formation;During drilling,hydration expansion and high formation friction cause frequent stuck drills and high time rate of borehole wall instability.Therefore,it is urgent to study and select treating agents such as inhibitors,plugging agents and lubricants for high-performance water-based drilling fluids based on the geological characteristics of the formation and technical difficulties in drilling construction in Marhu block.And so a high performance water-based drilling fluid system suitable for the geological conditions of Mahu block should be developed.The geological stratification of Marhu block is complex,and the inclined section is mainly located in the Kerxia formation and Baikouquan formation,which contain high argillaceous sandstone.X-ray diffraction was used to analyze the minerals in the block,and it was found that the content of clay minerals was 6%-50%,with great lithology difference and strong heterogeneity.The content of aemon mixed layer is up to 25%-36%,and the content of expandable clay minerals is high,which is prone to hydration expansion and dispersion.Scanning electron microscope（SEM）results showed that the rock samples in this area have fine shale,some cores have obvious micro-fractures,and the cementation degree of the stratum is low.The results showed that the pore throat radius of the block was 0.2-2.4m,the porosity was 8.14%-12.76%,and there were obvious microfractures.Therefore,the mechanism of borehole wall instability in Mahu block can be summarized as follows:the formation is highly heterogeneous and the clay mineral content is high;the formation has fractures and weak bearing capacity.As well as the drilling process is prone to shrinkage and stuck drilling problems,resulting in the block wall instability complex time rate is high.To solve the problems above,the crucial agents specific HPI and HPB have been selected in this research,both performance of which is superior than the common treating agents.HPI aggregates bentonite sheets to form extremely thick particles,thus inhibiting clay hydration dispersion and hydration expansion.HPB can form a thin film on the surface of the borehole wall,which can be plugged during drilling and removed during production to stabilize the borehole wall.Meanwell the auxiliary agents include lubricant and encapsulant and compound filter loss reducer also have been selected to coordinate the formula performances.The laboratory tests showed that the performances of the high performance drilling fluid is fit for Mahu well block.The basic formula of the system is as follows:3%Bansoo slurry+0.5%Na OH+1%compound filter loss reducer+2%blocking agent HPB+2%inhibitor HPI+1%lubricant HPL+0.5%encapsulant PMHA-2+10%Na Cl+barite(1.70 g·cm^-3).The formula of drilling fluid can be adjusted flexibly by different geological features.The adjusted drilling fluid formula was used in 9 wells of Mahu18 well block and 2 wells of Xiquan well block and 1 well of Jimusaer well block.Field application data showed that high performance water-based drilling fluid system could effectively maintain the lake piece of borehole wall stability,at the same time could rise the lubrication effect,thus reducing the complex accident,shorten the drilling cycle,improving the economic benefit.Moreover,the application of high-performance water-based drilling fluid in two Wells in Xiquan well area and one well in tight well area was also good,which solves the problems of borehole wall instability and easy jamming during drilling,and had a good prospect of application.