Study On Acid-Fracturing Technology Of Carbonate Reservoir Of Lower Paleozoic In Ordos Basin

The gas resources of carbonate reservoirs of Lower Paleozoic in the Ordos Basin are rich in natural gas resources.The total resources are 2.55 trillion square meters,which has great potential for production.It is an important field for the development of gas fields in China.However,the depth of the reservoir is 3700m?4000m.The closing pressure is 55MPa?70MPa.The average formation temperature is about 120?.The reservoir type is relatively complex.The heterogeneity is strong,and the filling degree is higher and denser.As such,it is difficult to promote the production and transformation.The results of preliminary gas testing in this area show that the proportion of low-yield wells is high,and some wells have not achieved production requirements after conventional acid-fracturing.Using volumetric transformation technology of foreign shale gas and domestic compact oil and gas,this article adopts volumetric acid-fracturing to promote production and transformation,and proposes a new working fluid system suitable for target reservoirs.The flow conductivity experiments and making the simulation of the flow conductivity of the complex fracture network optimize the acid-fracturing process parameters,improve the acid-fracturing construction quality and provide theoretical guidance and technical support for the production and transformation of this carbonate reservoir.It is of theoretical significance for the stimulation of similar low-permeability dense carbonate reservoirs.The specific details are as follows:(1)Based on the relevant evaluation methods of shale gas volumetric fracturing,this paper carries out adaptive evaluation of the target reservoir for volumetric acid-fracturing,natural fracture development characteristics,rock microstructure,rock brittleness and horizontal principal pressure difference.(2)Analyzing the requirement of the working fluid system for the target reservoir and acid-fracturing process,the paper optimizes the characteristic of the three different functional systems of the fluid system for creating fracture,the acidizing fluid system for etching fracture and the acidizing fluid system for etched channel so as to form a new set of adapted working fluid system.(3)This paper observes the dynamic etched morphology of rocks in different acid systems,and analyzes the acid-rock reaction and non-uniform etching conditions.The flow conductivity of each acidizing fluid and etched morphology of the rock are analyzed contrastively according to different types of acidizing fluid,acidizing fluid levels,acidizing fluid concentrations,closing pressures,and multiple stages of alternate injections.(4)Combining the criteria of intersecting interactions,the paper constructs a complex fracture network extension model for volumetric acid-fracturing,acid flowing of it,and sets up the model of flow conductivity as the target model.Then the process parameters such as the displacement of the working fluid,the acidizing fluid levels,and the number of stages of multiple alternative injection technology are optimized.