TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper presents an algorithm to optimize the production and shut-in periods of plunger-lift based on reservoir performance. The algorithm combines analytical models of reservoir and wellbore fluid flow. The implementation of the algorithm requires a relatively simple and inexpensive electronic control system. The new system may be connected to existing wellheads with minimal modification. One of the advantages of the new algorithm is the ability to automatically incorporate the changes in the line pressure. An example application is presented to indicate that the new algorithm may increase plunger-lift production by a factor of two.
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 an 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. This particular behavior has been addressed with different names: de-watering, reverse coning, to name a few. We call this behavior ROC (retrograde oil cut) mechanism. Our goal is to explain various anomalous behaviors in the field production, which can be reproduced by geologically defensible reservoir model. We tested several models by comparing the field data with the simulated behavior. Finally, we converged on to a three-layer model - which is geologically and core data consistent - and can produce various anomalous characteristics. These include decrease in WOR over time, increase in GOR after the well has been shut-in, long transient state behavior of oil production, and the decline in pressure (instead of pressure build-up) after some of the wells have been shut-in for 24 hour periods. We have integrated available core and log data, relative permeability data, geological understanding as well as PVT data to build this model. We tested this model by mimicking production from several wells in West Carney Field in Oklahoma. The implications of understanding the mechanism are enormous. Although we only concentrated on Hunton Formation in one county, Hunton formation extends over 2 million acres in Oklahoma alone. Similar formations also exist in other states, which were deemed unproductive in the past. By correctly understanding the production mechanism, the viability of producing from other similar formations can be better investigated. Introduction The objective of this study was to establish a primary production mechanism by which oil is being produced from the Hunton formation by incorporating engineering and geological information. Hunton formation, though promising in nature, has not been fully developed because of its anomalous behavior. Initially, field development was sporadic and many of the earlier wells were abandoned due to high water production and limited surface facilities for disposing off the excess produced water. With the depletion of the reservoir, oil cut increased, making it feasible to develop the field. Hunton Formation covers approximately 2.7 million acres in Oklahoma1 (Figure 1a) and in surrounding states of Texas, Arkansas and New Mexico. We concentrated our study to one county, West Carney county, in Oklahoma (Figure 1b). Formation is highly fractured and discontinuous and local variations in geology affect the performance to a great extent. Properties observed at the wellbore are sometimes misleading and the well behaves contrary to the observed properties. Some of the unique characteristics of the field are decrease in WOR over time, increase in GOR after the well has been shut-in, decline in pressure (rather than pressure build-up) after some of the wells have been shut-in, and long transient state behavior of oil production. We have tried to explain these unique characteristics using numerical model and the results from this could be extrapolated to other fields producing in a similar manner.
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.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe paper describes an
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