Abstract

This paper discusses the design, implementation, and results of a new completion method to eliminate bottom water coning. This method uses a dual completion in the same zone to produce water-free oil at higher rates than conventional completions. This is accomplished by producing water from perforations below the oil-water contact, at the same time that oil is being produced from perforations at the top of the sand. The method is currently being used in the Nebo Hemphill Field in North Louisiana. Mathematical models are used to assist in the design of this completion. With this modeling, the perforation spacing is determined, along with an estimate of the water production needed to prevent coning. The first well to use this new completion method has been on production for over a year. This paper documents the production rates, and economic success of the test well using this completion method.

Introduction

For years, one of the main problems encountered in oil and gas production has been the production of associated salt water. This problem increases operating costs, and decreases revenue in most cases. This is primarily due to several factors:

  1. Larger tubulars and/or more expensive artificial lift systems are needed to handle the increased production volume caused by water production,

  2. Separation of the water from the oil, at the surface, requires large initial investments, and daily expenditures over the life of the well and,

  3. Increasing water/oil ratios lead to decreased production, lower revenues, and possibly lower ultimate recoveries.

All of the above problems are present in the Nebo-Hemphill Field located in LaSalle Parish, Louisiana. Oil in this field is produced from Wilcox sands that are well known in the area for their high water cut production. Most of these sands have very strong natural water drives, and many oil reservoirs have an O/W contact with the water column making up 10 to 90 percent of the height. This leads to bottom water coning that takes place very rapidly due to the clean nature of many of the sands. These clean sands have 1 to 4 darcy permeability, and very high vertical to horizontal permeability ratios.

One of the most severe bottom water coning problems encountered in this field occurs in the unconsolidated Top of Wilcox sand. At approximately 2500', the oil is much more viscous than the produced water. A conventional completion (which consists of perforating the top of the sand and gravel packing) begins to cone water within 4 months, even though the production perforations are 15' above the original O/W contact and the well only produces 30 BOPD This severe coning problem continues and leaves a conventional well making only 10-25 BOPD at 10:1 or greater water/oil ratio after only 2 to 3 years. Any attempt to produce more total fluid yields an increase in water cut that quickly diminishes any increase in oil production. These low production rates along with high water cuts lead to only 15 to 25 percent ultimate recovery of OOIP.

For these reasons, a new completion method was designed to increase oil productivity and increase the amount of oil ultimately recovered in this field. This completion exemplifies the principles of the in-situ-segregated production method. The Top of Wilcox sand was selected to be the first place that the newly designed water drainage-production system would be tested. The objectives of this field trial were as follows:

  1. Prove that the theory works by producing well at constant oil rate for at least 6 months without coning water.

  2. Produce at initial rate in excess of any past sustainable rate from surrounding wells.

  3. Produce oil directly to sales tank without any treatments to remove BS&W.

  4. Produce saltwater directly to disposal system without any treatments to remove oil.

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