In Permian Basin unconventional reservoirs, field production data show that water cuts tend to increase over the long term, mostly driven by depletion. This increase becomes more severe with faster reservoir depletion due to larger completion designs, higher well density, and more aggressive production techniques. This study examined water cut increases over time and developed a methodology to predict water production more accurately using production diagnostic tools and numerical simulation.
A comprehensive workflow is introduced to forecast the water production rate. First, type wells are selected to represent a certain bench in a field, and then production history is matched with numerical simulation. With the forecast from the calibrated simulation model, a new correlation of the water cut trend can be generated. In this correlation, a dimensionless production parameter is introduced to correlate water cut and oil production better, considering different pressure depletion profiles, operation strategies, and stimulated reservoir volumes (SRV) among the wells. The water cut correlation is compared and adjusted with all analog wells in the field, and then it is ready to be used to forecast water rates in the same wells or analogs.
With this novel workflow, water cut correlations can be generated for each field and each formation. By considering reservoir depletion in the new dimensionless parameter, the new correlation predicts the water cut trend more accurately than other diagnostic tools or analog wells. The new correlation can be used to generate a water production forecast as a type well for a particular field or well given an initial water cut. Improved water production forecasts could aid in surface facility design, water disposal management, water handling cost evaluation, and reserve estimates.
In Permian unconventional fields, the field development and production strategies have improved tremendously over the past decade. Operators have drilled longer lateral wells (Han et al., 2021), applied larger fracture sizes (Uddin et al., 2019), placed more wells per section, and flowed back more aggressively and efficiently (Xie et al., 2021). As a result, the newer wells have achieved higher initial production rates. However, field data show that water cut increases faster with the latest development and production strategies (Jacobs, 2016). Amadi et al. (2022) investigated the causes of increasing water cuts in Permian Basin unconventional wells using field data analysis, theoretical analysis, and reservoir simulation. That study found that while drilling and fracturing into wet zones will result in a high water cut, the increase over time is not because of a mobile aquifer or a wet zone completion. Rather, the increasing water cut trend is mostly because of improved completion methods, increased well density, and aggressive production techniques that speed up fluid withdrawal rates. Without pressure maintenance from the injection, gas cap expansion, or aquifer influx, changes in water cut are controlled by changes in fluid properties, saturation, and effective permeability with pressure depletion. The trend is normal for a volumetric oil reservoir under solution gas drive.
