Prediction model for fracture width changes in vug-fracture oil reservoirs and its application

Key words:  vug-fracture oil reservoir  length of fracture  lateral pressure coefficient  fracture dip  prediction model

Abstract:

In vug-fracture oil and gas reservoirs, the fractures are not only the main reservoir space, but also the seepage channels between the vugs and caves, so the opening and closure of the fractures have an important influence on oil and gas production. In order to predict the variations of the fracture width, a finite element mechanical model was established, based on the geological data from Tahe Oilfield, considering the change of internal pressure, in which the closure process of the fractures under different conditions can be simulated. The effects of various factors on the closure of fractures were analyzed via an orthogonal testing method. Based on multivariable regression analysis, a model to predict the variation of the fracture as a function of fracture dip, fracture length and lateral pressure coefficient was established. The simulation results show that fractures with a longer length and a larger lateral pressure coefficient are more vulnerable for closure. The effect of fracture dip on fracture closure can be influenced by the local stress distribution. In the strata that the tectonic stress is smaller than the vertical stress, the fractures with smaller dip are easier to close. The lateral pressure coefficient has a larger effect on the closure of fractures than that of the fracture length and fracture dip.