Improvement of Production Data Analysis Method for Shale Gas Wells

Abstract Rate normalized pressure (RNP) and derivative (RNP') method uses the log-log plot of RNP and RNP' versus material balance time (te) to interpret formation and hydraulic parameters like permeability and fracture half-length. It's a very useful methodology and sometimes the only way to conduct transient rate and pressure analysis for shale gas wells because pressure buildup is rarely recorded. However, the method may be not applicable because material balance time is not a monotonic increasing function of time especially when the one well has a short production history and has big vibration of production rate. A new method is proposed to solve the above problem for shale gas wells. In the new method, the average material balance time (cumulative production (Np) divided by average gas rate) is used to replace te. Therefore, the increasing monotonicity with production time is guaranteed. Curves of te vs. production time and average te vs. production time are contrasted. Different field cases with smooth decreasing gas rate and the cases with sharp change rates are used to check the applicability for the proposed new method. The plots of RNP & RNP' vs. average te, RNP & RNP' vs. te are drawn for different shale gas wells data for accuracy comparison. Results show that the new method has similar type-curve with the RNP & RNP' vs. te method and can be used to interpret the formation and hydraulic parameters by diagnosing typical flow regimes for shale gas wells. Compared with the RNP & RNP' vs. te method, the new method theoretically improved the accuracy production date analysis because the x axis is a monotonic increasing function of production time while not showing inflection points in RNP & RNP' vs. te plots. Field case with smooth decreasing gas rate shows that the new method and RNP & RNP' vs. te method can both get satisfactory log-log plot match and rate & pressure history match. Although the RNP & RNP' vs. average te may give smaller SRV volume, the interpretation results for both methods are comparable. The shale gas case with sharp vibrated gas rate shows that the new method can get both better log-log plot match and rate & pressure history match, in return, the interpretation results may be more confident. The RNP & RNP' vs. average te method may improve the production data analysis (PDA) accuracy when the shale gas wells have huge rate vibrations which may be caused by fluid flow-back, choke size change, temporary well shut-in and etc. However, more shale gas wells data should be used to test the method.