Improvement And Research Of Acid Fracturing Design Model And Sensitive Factors Analysis

Acid fracturing is one of the most important production technical for lowpermeability reservoirs, especially for the low permeability carbonate reservoirs. It iscommonly to evaluate the results of the acid fracture by two aspects, the flowconductivity of the acid etching fracture and effective distance of live acid. Both ofthem are closely related to the reaction process in the rock fracture. When acid flow inthe fracture, not only the reaction between acid and rock, but also the leak off ofwormhole, finger advance of acidizing fluid and others complexly physics andchemistry phenomenons.Due to those phenomenons,the acid pressure optimizationdesign model is very complex. Both of the domestic and abroad scholars have donedecades of research for acid rock reaction mechanism and acid fracture design model,there are still many problems that have not been resolved. In the present, the extensiveuse mathematical model of acid flow reaction has too many assumptions, some factorsin the actual production which would effect the calculation of acid fracture designmodels were not considered.In the process of acid fracturing, chemical reaction produces between acid androck wall, the acid concentration in the reaction process gradually reduce untilreaction completely. At that time, the final acid fractures were formed. However,when acid being jumped into formation from the ground, the temperature betweenacid and formation are difference, the convection heat transfer and diffusion wouldaffect the temperature of acid. In this process, reaction speed between acid and rock isunder environmental temperature control, the speed is from fast to slow. In addition,the flow of the acid and rheological properties in the dual role of shear and thetemperature will generate a large negative effect, for example, crosslinking acid formula (cross linking agent, gel breaker concentration) would be set by gel breakerand reasonable return discharge time, which all depends on the environmenttemperature.In the reaction process between acid and rock, the reaction heat which willincrease the temperature of the acid itself, and finally affect the results. In order topredicate flow temperature profile of acid in the formation and acid concentrationdistribution in the fracture more accurately, the increase of the reaction heat must beconsidered. This paper will add reaction heat into fracture rock wall energy equation;attain a mathematics model of acid concentration distribution with the considerationof reaction heat calculated. The model considers the flow of acid along the fracturelength, and the convection spread along the width. Coupling the heat balance equationand acid reaction equation to get a solution, it can predict acid concentration andtemperature alternation along the length fractures. Take a calculation and simulationto one well in Jungian using the experiment to obtain the cross-linked Acid RockKinetic Parameters and cross-linked acid Jungian field acid fracturing sand carryingconstruction parameters, simulation results show that the reaction heat has a greatinfluence on temperature profile and the influence on effective distance is obvious.And then, the paper analyzed the sensitivity of the research of the parameters the withthe reaction heat considered. This paper calculated the different formation temperature,acid concentration and reservoir types on the influence of effective distance, and theimpact factors of parameters according to the construction of the construction siteresults, some suggestions were put forward, which can provides the basis for acidfracture design and expected result of construction in carbonate reservoirs.