Field Application of In-Situ Gravity Segregation to Remediate Prior Water Coning
Authors: Bowlin K.R. , Chea C.K. , Wheeler S.S. , Waldo L.A. 
Published: December 2007

Many oil and natural gas producing wells suffer from a phenomenon know as "water coning" wherein a water saturated formation underlies the hydrocarbon bearing formation without any impermeable barriers separating the water and hydrocarbon. In the process of withdrawing hydrocarbons from the formation, the underlying water is drawn by viscous forces into the hydrocarbon bearing section when conventional completion techniques are applied. In-Situ Gravity Segregation (IGS) is an alternative completion technique that mitigates the effects of water coning. This method entails producing a significant volume of water through perforations in the well casing (water sink) below the OWC surface concurrently with producing hydrocarbons through perforations in the well casing (hydrocarbon sink) above the OWC surface. Producing water below the OWC tends to suppress the creation of the water cone, thereby protecting the hydrocarbon section from water invasion. Essentially, the downward viscous forces imposed by withdrawing water from beneath the OWC balance the upward viscous forces imposed by withdrawing hydrocarbons from above the OWC. By using this technique, the hydrocarbon rates can be improved greatly over conventional critical oil rates associated with water coning.

Based on current literature, the IGS completion technique has been successfully implemented on new completions with no prior history of coning. This paper focuses on the application of IGS completion technology to a well located in Kern County, California that had over 10 years of prior water coning in an attempt to mitigate existing water coning problems. A numerical reservoir simulation model was used to aid in the design of completion and production rates. Design, implementation, and field results will be presented along with performance predictions from reservoir simulations.

Introduction

When wells are partially completed in an oil column that overlays a water column without sufficient barriers separating the oil/water contact (OWC), water coning can occur. The severity of the water coning problems is a function of the reservoir rock and fluid properties. Maximum water free oil production, termed critical rate, is typically below commercial levels and usually ignored.

Traditional approaches aimed at eliminating water coning are very poor. Various chemicals placed in the reservoir to form an artificial barrier to impede bottom water encroachment have been attempted in the past. There are many inherent problems associated with this approach. The main problem lies in economically placing a "pancake" in the reservoir of sufficient size to form a barrier needed to block water flow. Chemical treatments are ineffective and uneconomical for correcting or eliminating water coning.

A new completion method is aimed at mitigating the effects of water coning by introducing an additional pressure sink in the reservoir below the OWC. This approach has been successfully implemented on new completions to prevent the creation of a water cone.

There are numerous wells in the industry that have been suffering from this problem for a number of years. For this reason, this technique was applied to a well with prior water coning to determine the applicability under these conditions. This completion method was applied to an existing well in Kern County, California to determine if the water coning effects could be reversed to obtain incremental oil production and recovery.

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