Exploration and Production Technologies
Economic Implementation and Optimization of a Secondary Oil Recovery Process: St. Mary West Cotton Valley Unit, Lafayette County, AR

DE-FG26-00BC15254

Goal
Using a detailed reservoir model to be developed by current reservoir characterization practices, the project will make a comparison study of the economic optimization of secondary oil recovery processes in a nearly primary depleted, Arkansas oil field to identify the process that will provide the most efficient and least costly operation under field conditions. To provide successful economics in the operation of a secondary recovery project initiated late in the primary production phase, three issues must be managed: reducing injection system installation costs; reducing operating expenses during the fill-up period; and reducing the response time to increased production rates.

Performer
Strand Energy, L.C., Houston, TX

Background
The St Mary West oil field is geographically located in Lafayette County of southwest Arkansas and geologically situated in the Southern Arkansas – Northern Louisiana Mesozoic Basin. The field produces light sweet crude oil and associated gas from a sand-shale interval of the Cotton Valley formation of late Jurassic age. The reservoir is a single lenticular, sandstone body with a combination structural - stratigraphic trap. The oil pay lies at an average depth of 8,620 ft. The structure of the reservoir is simple with no apparent faulting and gentle dip of approximately one degree from the highest reservoir penetration to the lowest. The reservoir sand is encased in shale and draped north – south over a southwest plunging nose. Well control indicates the sand is discontinuous on the north and east sides and there is apparently a down-dip water column in the sand on the south and west sides of the reservoir body.

The St Mary West - Cotton Valley sandstone reservoir was discovered in 1984 while drilling a deeper prospect targeting the Smackover carbonates on the structural nose. The small field was developed quickly with ten oil wells drilled and completed in 1984 and 1985. Several dry holes defining the limits of the oil column were drilled on the north, west and east sides of the field.

The field has produced 975,000 barrels of light, sweet crude oil and approximately 1 BCF of associated natural gas. Oil production peaked at 20,000 barrels from eight wells for the month of March 1985 and current production averages 38 BOPD from two producers.

The oil is produced from a sandstone of good reservoir quality with an average porosity of 16 percent and permeabilities ranging from a few milidarcies to over one hundred milidarcies. The sand consists of clean quartz grains with little clay content. The production mechanism has been predominately solution-gas drive with possibly one well having an anomalously high primary recovery factor due to water encroachment on the oil trap by a down-dip aquifer.

Strand Energy (Strand) purchased substantially all interests in the St Mary West field in 1997 with the philosophy that for the long term continuation of economical oil production it would be necessary for reservoir management to become focused on secondary recovery processes. The St Mary West Barker Sand Unit (SMWBSU) was created in 2002 by unitization order of the Arkansas Oil & Gas Commission (AOGC) following several years of delay caused by one other active operator.

Strand completed design and installation of a pilot water injection system during the fall of 2003. The reservoir and wellbore injection performance data gathered during the pilot injection phase of the secondary project will be important to the secondary recovery optimization study for which the DOE grant was awarded. Recent water injection rates have averaged 440 BWPD into two pilot injection wells. Water injection rates for the Unit were improved with the addition of a second injection well and hydraulic fracturing of the reservoir sand in the injection wells. Cumulative injection to date for the pilot project is 581,000 barrels of water. Possible waterflood response is apparent in one producer located north of the pilot injection site. Currently the water injection system is being upgraded to provide for increased injection volumes.

Impact
A successful evaluation to choose the practical secondary recovery process appropriate for the St Mary West reservoir and the implementation of the project in the St Mary West field will aid in the development of skills in the small independent population for the future deployment of economical improved recovery projects in the mature oil fields operated by small independents throughout the U.S.

Results
Some preliminary results were developed during the project period that include reservoir and well bore injection performance data obtained during the pilot flood. The intent was that this data would provide important data for completing the planned reservoir model and optimization of the secondary recovery process. Overall project progress was slowed initially due to significant delays in the unitization of the field caused by delays within the Arkansas Oil and Gas Commission and subsequent ratification of the unitization of the Royalty Owners. Following these delays the project began implementation of work over efforts for the field (not in the scope of this project) and have continued with efforts associated with field workover and establishment of operations. As a result of these field activities and other activities of the Strand company related to its core business there was a lack of available personnel or time to dedicate to the activities specifically planned under the scope of this grant. Given these constraints, core work under the grant was never undertaken and the grant was ended in June 2008.

Current Status (January 2009)
The project has been ended. Core work, as planned under the grant, essentially was never undertaken in any significant fashion within the time frame in which the Grant existed due to limited availability of time and resources. Given the limited advancement of work under the Grant, a decision was made in June 2008 to allow the Grant to end without having completed the scope of work. Given this decision, no formal project report will be prepared or provided.

Project Start: July 1, 2000 
Project End: June 30, 2008

Originally planned DOE Contribution: $75,000
Actual DOE Contribution: $3,256
Actual Performer Contribution: $1,212,000

Contact Information: 
NETL – Jim Barnes (jim.barnes@netl.doe.gov or 918-699-2076) 
Strand – Cary Brock (713-658-8096)


SMWBSU water treatment facility is located 100’ north of SMWBSU #7-2 WSW and 40’ north of SMWBSU #7-1 initial injection well for the pilot injection project. Note high-low pressure control shut-down gauge (red) downstream of check valve.


Custom-designed and fabricated modular water filtration plumbing for easy transportation and setup being tested at independent fabrication shop, Clute, TX. Note stainless steel basket strainers are also custom-designed and assembled by fabricator. Jeff Ahern (shown) and Cary Brock were the designers.

 
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