Sandstone Oilfield Acidification Study

Daqing Oilfield is a typical multi-layer sandstone reservoir of continental facies. Early waterflooding is performed as field development regime to maintain production pressure. But some layers have poor water injectivity during water flooding due to severe heterogeneity, and acidizing measures are needed to reach injection allocation and economic development.Research on acidification started from 1963 in Daqing Olifield. After 42-years research and application, great achievements have been got on aspects of acid formula, additives and acidizing mechanisms. Acid-rock reaction is a multi-phase reaction that happens in porous media, different mineral produces different product and various degrees of formation damage when it reacts with acid . Originally, short cores are used to study reaction mechanism, by which description for near well-bore zones instead of the further research on the reaction in deeper formation can be obtained. Additionally, the influence of secondary precipitation, fine migration and adsorption on acidizing results cannot be gained. Therefore prediction for permeability variation in deep formation based on the experimental results by short cores sometimes will lead to lower effectiveness in field application.This paper presents the research on acid formula, simulated test of the acid-rock reaction, and numerical modeling for Pu-tao-hua strata of Daqing external oilfield. The key points of the research are as follows:1.Based on static acid-rock reaction, simulated flow test by a ?short and long core, residual acid ion concentration analysis by ICP, rock compressive strength determination, microcosmic analysis by ESEM, secondary precipitation analysis by energy spectrometer, research on microscopic pore configuration of sandstone before/after acidizing by constant speed intrusive mercury, mobile fluid saturation determination by NMRI, systematic sandstone matrix acidizing experimental methods for acid-rock reaction and secondary damage mechanism are established. Following conclusions are reached.