Experimental Study on Wall Stability of Acid-Etched Fractures Carbonate Reservoir

It is difficult to maintain the conductivity of acid etched fractures in deep carbonate reservoirs. The instability mechanism of acid etched fractures is analyzed by mineral composition analysis, laser scanning before and after acid etched, and continuous strength measurement. By determining the morphology and mechanical characteristics of the fracture wall, the construction parameters such as acid etched time and displacement can be obtained. The continuous strength of the same parts of the rock samples before and after acid etched was compared, and it was found that the strength of some areas increased after acid etched. The main reason for the increase in strength is that the calcite is dissolved by the acid solution, while the dolomite covering the bottom is exposed, and the dolomite strength is higher than the calcite strength. The compressive strength of the dolomite-containing part of the same rock is about 40∼50MPa higher than that of the calcite part. 1. INTRODUCTION As a reservoir with abundant oil and gas reserves, carbonate rock has become an important research object of oil and gas exploitation. Carbonate reservoir contains 48% of the world's oil and gas reserves. With the discovery of many deep and ultra-deep carbonate oil and gas fields in Tarim, Ordos Basin and other places, the exploitation of carbonate reservoir has become an important research aspect for increasing oil and gas storage and production in China, and acidizing and fracturing is the main technical means for increasing production of carbonate oil and gas fields. Acidizing fracturing technology is to press acid into the reservoir and form fracture s under conditions higher than the fracturing pressure of the reservoir. At the same time, acid of different systems can react with calcite, dolomite and other rocks on the wall, and non-uniformly etch the fracture wall to form support bodies of different heights. After the completion of construction, the support bodies can effectively support the fractures and make them not completely closed. Finally, a certain length of fracture with flow diversion ability is formed, so as to achieve a production increase effect.