Production Type Curves for the Hunton Formation

Abstract

Summary The Hunton Formation is one of the most promising formations producing oil and gas in Oklahoma. The formation has an anomalous producing behavior. At the inception, the wells produce at relatively high water-oil and gas-oil ratios. Eventually, both the WOR and GOR decrease. This results in increase in oil cut and hence reduction in lifting costs over time. Because of relatively high WOR's, many operators are discouraged from completing the wells, and hence abandoning the effort to produce oil from these formations. We concentrate on West Carney Field, Lincoln County, Oklahoma for this investigation. The field was "re-discovered" in 1995, and significant drilling activities continue in the field today. The field produces various amounts of gas, oil and water from each well. Because of varying gas oil ratios and water oil ratios over the field, a simple decline curve analysis is not applicable to determine the hydrocarbons in place. Attempts to calculate the reserves based on the electric log data have produced inconsistent results because of poor correlation between log signatures and productivity and connectivity of wells. In this study, we provide a technique for evaluating the performance of producing wells. Because the wells have variable rates and variable bottom hole pressures, we used the concept of equivalent time as proposed by Agarwal et al. (SPE 57916), and show that we can correctly predict the reserves estimate. Also, we show that it is possible, using Agarwal et al's equivalent time concept, to use automatic type curve matching to predict values of permeability and skin factor. We evaluate the gas, oil and water rates separately to calculate permeability and skin factor. We then use the results to estimate recovery factors and the quality of our initial completions. This type of analysis is useful for economic evaluation, planning of surface facilities, and future field development and exploitation. Further, if sufficient early production data are available, the procedure can also allow us to predict various reservoir parameters that can be used for additional evaluation. Introduction The West Carney Field initially produced very high water rates and low oil rates, but over time the WOR decreases providing for an increase in oil rate. The water rate slowly declines and eventually goes to zero in some cases. With high water rates come high lifting costs, so a good estimate of reserves is needed to determine the economic feasibility of the field. With this strange behavior, however, conventional methods for estimating reserves and reservoir parameters (permeability and skin) can no longer be calculated with confidence. A new production decline method is needed to accurately estimate reserves and reservoir parameters to adequately develop and exploit of the West Carney Field. Because the wells are produced at variable bottomhole pressures and variable rates, we have used an equivalent time approach presented by Agarwal et al. This paper, however, introduces the use of automatic type curve matching using the Levenberg-Marquardt algorithm. It will be shown, using synthetic data as well as one field example, that using Agarwal et al's equivalent time and nonlinear regression type curve matching can yield extremely useful results. The production for the three fluids is analyzed separately, allowing for reserve, permeability, and skin estimates for each of the three fluids.