Research and Application of Fuling Shale Gas Anti-Collapse and Anti-Leakage Drilling Fluid System

Aiming at the problems of microfracture development in hard brittle shale gas layer in Fuling block, Chongqing, such as collapse of borehole wall and the existence of permeability loss of microfracture during drilling, and serious pollution of drilling environment with oil-based drilling fluid, a water-based drilling fluid system for anti-collapse and anti-leakage was studied. A water-based drilling fluid system with anti-collapse and anti-leakage was formed by introducing functional treatment agents, such as polypolysaccharide MEG, polymer emulsion film forming wall cementing agent LFGB, polyamine inhibitor LCFA and deformable particle plugging agent BXLZ, into the conventional water-based drilling fluid. After rolling at 130°C for 16 h, the system has good rheological properties, low filtration loss, good inhibition, lubrication and plugging properties. It has good plugging properties for 0.12 mm, 0.24 mm, 0.38 mm micro-cracks and 400 mD and 800 mD sand plates. The system was successfully tested on site in August 2019 in Fuling Reef Block, showing good rheological properties, solid wall plugging, and strong ability to seal and inhibit fracture expansion. There was no block falling in the drilling process, and the tripping, casing running and well cementing operations were all smooth, which provided a new technical idea and scheme for environmental protection and green drilling in Fuling shale gas exploitation.

Development and Application of TL-1 New High Temperature and High Pressure Plugging Instrument

In view of the fact that most of the filter media of existing plugging evaluation instruments use steel plates or steel balls, which cannot truly simulate the characteristics of the formation, a new type of TL-1 high temperature and high pressure plugging instrument has been developed. The filter medium of the instrument is the natural stone with different cracks and quartz sand beds with different particle sizes, which can better simulate the adsorption and hang-up effect of the formation on the plugging agent. It is possible to evaluate the plugging effect, pressure-bearing capacity and return pressure of the plugging slurry for different cracks and sand beds of different sizes under different temperatures and pressures. Using new and old instruments to evaluate the plugging effect of the same plugging slurry, it is found that the plugging effect is different from the distribution of the plugging material on the crack surface, the plugging effect and the pressure bearing capacity. The instrument is stable and reliable in operation and simple in operation. It is a new instrument for conducting research on anti-leakage plugging materials and anti-leakage plugging drilling fluid systems.

The Research of Polymer Film-Forming Plugging Agent for Drilling Fluid

In order to improve the plugging and anti-collapse performance of water-based drilling fluid,a polymer film-forming plugging agent LWFD is synthesized by emulsion polymerization.The effect of the agent on rheology,API filtration loss,lubricity and film plugging of polymer drilling fluid and cationic drilling fluid is evaluated in laboratory.The experimental results show that the agent has little effect on the rheology and filtration loss of polymer drilling fluid and cationic drilling fluid,and can improve the lubricity of drilling fluid.The synthesized polymer film-forming plugging agent LWFD has good plugging properties for sand discs with different permeabilities,and the agent can effectively improve the film-forming plugging and temperature resistance of drilling fluid when combined with the inorganic nano-plugging agent NMFD.The high performance polymer drilling fluid formed by introducing polymer film-forming plugging agent LWFD and inorganic nano-plugging agent NMFD into polymer drilling fluid has comparable performance as Halliburton’s SHALEDRIL high performance drilling fluid,which can meet the requirements of on-site drilling and has application value.