Rheological property of low-damage,ideal packing,film-forming amphoteric/sulfonation polymer drilling fluids

Low-permeability dense reservoirs,including micro-fractured reservoirs,are commonly characterized by high content of clay substances,high original water saturation,high sensitivity to invasive fluids,high capillary pressure,complicated structure and anisotropic,high flow-resistance and micro pore throats etc,.Generally they also have lots of natural micro fractures,probably leading to stress sensibility.Main damaging factors in such reservoirs are water-sensibility and water-blocking caused by invasive fluids during drilling and production operations.Once damaged,formation permeability can rarely recovered.Numerous studies have shown that damaging extent of water-blocking ranges from 70% to 90%.Main damaging mechanisms and influencing factors of water-blocking were systematically analyzed.Also some feasible precaution or treating approaches of water-blocking were put forward.In a laboratory setting,a new multi-functional drilling fluid composed mainly of amphion polymer,sulfonation polymer,high effectively preventive water-blocking surfactants,ideal packing temporary bridging agents(TBA) and film-forming agents,etc.,were developed.New low-damage drilling fluids has many advantages,such as good rheological properties,excellent effectiveness of water-blocking prevention,good temporary plugging effect,low filtration and ultra-low permeability(API filtration≤5 mL,HTHP filtration≤10 mL,mud cake frictional coefficient≤0.14,permeability recovery>81%),can efficiently prevent or minimize damage,preserve natural formation and enhance comprehensive development-investment effect in TUHA Jurassic dense sandstone reservoir formation with low-permeability,the only one developing integrated condense gas field.Some references can be provided to similar reservoir formations.

A reservoir drying method for enhancing recovery of tight gas

Based on the study of damage mechanisms of generalized water blocking and related water-blocking removal methods, the drying agents for enhancing tight gas reservoir recovery were developed, and the basic properties, injection mode and drying effect of the drying agents were evaluated. The chemical effect, thermal effect, salt resistance, salt resistance formulas and delay mechanism of the drying agent systems for different types of tight reservoirs were investigated through lab experiment. The solubility and solubilization properties of supercritical carbon dioxide on drying agent systems were tested.The injection mode of dissolving drying agent in supercritical carbon dioxide was proposed. The mechanisms of supercritical carbon dioxide with water in micropores of formation matrix were analyzed. Micro-pore structures and seepage characteristics of reservoir before and after drying were compared. Based on the characterization in combination of NMR and laser etched pore structure model, drying effects of the drying agents on bound water of different occurrences were evaluated qualitatively and quantitatively. Lattice Boltzmann method was used to evaluate the influence of drying effect on gas micro-seepage ability.The influence of drying effect on productivity and production performance of gas well was analyzed by numerical simulation.The drying effect can greatly reduce water saturation of tight reservoir and improve the gas seepage capacity in near wellbore and fractures. This work can provide guidance for developing new measures in enhancing recovery of tight gas reservoirs.