Hydroxyl Urethane Guar Damage To Quartz Pore Blockage

With the large-scale oil and gas exploration and development, the conditions of the remaining sandstone gas reservoirs resources in China is relatively complex and poor. Hydraulic fracturing has become an indispensable technique to dramatically increase single-well drainage area, stimulated reservoir volume (SRV), and hence, maintain sufficient flow rate to satisfy the increasing domestic demands of oil and gas resources. During the fracturing process, however, the leakage of macromolecular thickening agent within fracturing fluids, from fracture surface to matrix, may block the pore throat in the invaded zone because of molecular adsorption and retention in the pore. And this is a reason that causes poor post-fracturing performance. At present, researchers pay little attention to the damage caused by the adsorption and retention of hydroxypropyl guar gum (HPG) in micro-pores and have vague idea about damage mechanism, and no targeted method has been proposed to solve these problems. Given these discrepancies, systematical investigations are need.This thesis, as part of major oil and gas project of 13th Five-Year Plan "Studies on desorption agent and low damage fracturing fluids technology", used porous media consist of quartz as subjects for this study, focused on the damage generated by adsorption and retention of HPG in quartz pore throat. Through the optimization of anthrone colorimetry, formed a method to measure the quantity of HPG adsorption and retention. Based on accurate measurement of adsorbed amount of HPG, the static adsorption experiments reveal adsorption force between HPG and quartz, and analyze the adsorbed amount variation with HPG concentration, pH and solution temperature. The dynamic retention experiments show the influence of pore structure, fluid parameters, projecting parameters on HPG retention damage. On the basis of clear understanding blocking damage mechanism, targeted proposes measures to reduce pore blocking damage by HPG adsorption and retention, and this can provide the basis for the research of low damage fracturing fluid technology.The static adsorption experiments result show that the adsorption force between HPG and quartz surface is hydrogen bonds, and the adsorbed amount of HPG increased with the increases of solution concentration and pH, and when pH between 5 to 7 and 10 to 13, adsorption amount increased obviously. When solution temperature increased from 75? to 95?, the adsorption amount drastically reduced. The dynamic retention experiments result show that the relative size between HPG particle size distribution and pore size distribution is the main reason of mechanical trapping. The HPG solution viscosity and the particle size increased with solution concentration increases, causing HPG mechanical capture probability and viscous resistance increased, resulting in HPG retention amount increased. When pH between 10 and 13, HPG molecule chains gradually become curl and disorder, and particle size increased with pH increases, resulting in HPG retention amount increased. When temperature increased from 70? to 120?, HPG retention amount decreased with viscous resistance decreases. Permeability damage reduced with flowback time and gas rate increases, and when fluid flow rate increased from 12mL to 18mL on the experiment condition, permeability damage obviously increased. Therefore, control HPG solution parameters and projecting parameters can effectively reduce pore blocking damage. Meanwhile, add suitable additives into HPG solution can also reduce permeability damage. Research results show that adding 500mg/L desorbent into HPG solution, the permeability damage reduced about 5%, and adding 500mg/L ammonium persulfate into HPG solution after reacting 60min at 70?, the permeability damage reduced about 20%.