Estimating formation and fracturing water production using simple diagnostic plots

The main goal of this paper is to evaluate the possibility of distinguishing between formation and fracturing water based on the water-flowback response without analyzing water chemical data. We analyze flowback production data of 100 multi-fractured horizontal oil wells completed in the Montney Formation and 89 oil and gas wells completed in the Duvernay and Horn River formations. We hypothesize that 1) the slope of waterflowback harmonic decline (HD) profiles (mHD) is proportional to the slope of rate-normalized pressure (RNP) plots (mRNP), and 2) both mRNP and mHD are inversely proportional to the amount of water influx from matrix into fractures. To verify our hypothesis, we 1) extend the previous HD and single-phase flowing material balance models by considering the water influx from matrix into fractures, 2) classify the studied wells based on observed trends, 3) construct RNP diagnostic plots of the studied wells, 4) investigate the relationship between mHD and mRNP, 5) analyze log data and estimate average initial water saturation (Swi) for the studied wells, and 6) investigate the relationship between of mHD and Swi. The results show that mHD for all the studied wells ranges from 0.00001 to 0.036 1/ m3 with a mean value of 0.0056 1/ m3. Wells with higher mHD have relatively higher mRNP values. In contrast, wells with very low mHD show no significant decline in water rate through the entire flowback process and relatively low or inconsistent mRNP values on the corresponding plots of RNP versus material balance time (MBT). We also observe a negative correlation between mHD and Swi obtained by analysis of wireline log data. This correlation and the positive correlation between mHD and mRNP indicate that as Swi increases, water influx from matrix to fracture increases, and thus, both mHD and mRNP decrease. Based on our modified models and the observed correlations, we develop a method to approximately differentiate between formation and fracturing water. The applications of our heuristic method on field data shows that 1) fracturing water production dominates the total water recovery for wells with higher mRNP, and 2) formation water production dominates the total water recovery for wells with lower mRNP.

Automated summary

The main objective of this paper is to differentiate between formation and fracturing water based on water-flowback response. By analyzing production data from different wells, the authors develop a method to classify the wells and investigate the relationship between different variables. The results show correlations between mHD, mRNP, and other factors, allowing for the approximate differentiation of water types.