| Acid fracturing stimulation technology is one of the main technologies for complex carbonate reservoirs to exploit,stabilize and increase production.Acid fracturing can form a certain length of artificial fractures with certain conductivity in the reservoir.The conductivity of acid-etched fracture is closely related to the productivity of oil and gas wells.Therefore,it is helpful for the evaluation of acid fracturing stimulation objectively to accurately calculate and effectively predict the fracture conductivity.Through the survey and summary,it is found that there are many factors affecting the conductivity of acid-etched fracture,including geological characteristics and engineering parameters.The predecessors mainly analyzed the influence of one or two factors on the diversion capacity by single factor quantitative and multi-factor qualitative analysis,then established a prediction model based on the incomplete investigation factors.However,the prediction model of diversion capacity under the influence of multi-factors has not been studied too much,which leads to a large error between the predictive results of the existing model and the reality.On the basis of a large number of literatures at home and abroad,we select dolomite which accounts for a large proportion of carbonate reservoirs in China to study the prediction model of acid-etched fracture conductivity.The single well data and cores for simulation and experiment are selected from the middle combined dolomite reservoir of Mawu Member in Ordos Basin.The role of fracture in reservoir,theoretical calculation formula of fracture conductivity,geological characteristics and engineering parameters affecting acid-etched fracture conductivity are summarized.The acid fracturing of dolomite reservoir is stimulated by the Meyer fracturing simulation software.The simulation results are compared with the indoor test results.The single factor analysis method is used to analyze the influence of logging parameters,physical parameters and engineering parameters on the acid-etched fracture conductivity,and the main control factors are obtained by partial correlation coefficient method.The relationship between main control factors and acid fracturing conductivity is fitted by ACE algorithm,and a prediction model of acid fracturing conductivity under the influence of multiple factors is established.The main achievements and understandings are as follows:(1)The results of the Meyer simulation and the laboratory experiments are compared and analyzed.It is found that the conductivity of the two methods is not significantly different,with an average difference of 8.61%.This result shows that the simulation results of acid-etched fracture conductivity are reliable for the analysis of effective factors of conductivity and the establishment of prediction model.(2)Through single factor analysis,it is found that there are complex,fuzzy and uncertain correlations between logging parameters,physical properties parameters,engineering parameters and acid-etched fracture conductivity.Therefore,a multi-factor mathematical analysis method is further selected.(3)The calculation results of partial correlation coefficient show that the main controlling factors affecting the acid fracturing conductivity are acid volume,resistivity,total fluid volume into well,injection rate and interval transit time(partial correlation coefficient > 0.2).It can be seen that the engineering parameters have a high degree of influence on acid-etched fracture conductivity.(4)The regression function relationship between fracture conductivity and main controlling factors is obtained by using ACE non-parametric regression algorithm,and a prediction model of fracture conductivity under the influence of multiple factors is established.The model validation results show that the prediction model of conductivity is reasonable and it can be used for the prediction of acid fracturing conductivity. |
