PRODUCTION REVIEWS PAYOUT QUICKLYFOR TWO TEXAS OPERATORS

T. Porter Tremble
Merit Energy Co.
Dallas
Jay Haskell
Schlumberger Wireline, Testing & Dowell
Houston

Two examples illustrate how focused reviews can enhance production from underperforming producing properties.

Identifying underperforming wells is the first step towards maintaining optimum performance from producing properties. The second is to ensure that any enhancement will have reasonable payout time.

These steps require trained professionals, production and economic analysis tools, production enhancement services, dedicated time, and a focused strategy. Schlumberger Oilfied Services organized a production enhancement group (wire line, testing, and Dowell personnel), to help operators identify and optimize underperforming wells.

The evaluation strategy employed in the two examples included collecting, cataloging, and thoroughly evaluating all data existing on the given well, or field, to identify any underperforming zones or wells. New downhole data and additional tests were acquired when needed for adequate formation evaluation.

Reviews included a list of services that can enhance production, the likelihood of success of these steps, and the economics. Only enhancement procedures with a strong likelihood of paying out within 6 months were recommended.

FIELD ENHANCEMENT

In early 1993, Merit Energy Co. let Schlumberger's production enhancement group review one of Merit's South Texas gas fields, La Reforma. At the time, Merit was conducting a preliminary field study. The production enhancement group expanded on Merit's work to determine if the field was performing to maximum potential. If not, the most economical options for improving production were to be identified.

Terms of the agreement called for all field data to be available to the production enhancement group for review. The review would be paid for by any subsequent field enhancement services performed. As with all production enhancement group projects, recommendations from the review would be tied to economics. Only enhancement services that would payout in 6 months or less would be recommended.

All log and production data for La Reforma field were collected. The field's five wells (Fig. 1) (27215 bytes) were then evaluated for potential production improvements using history matching, Nodal analysis, and log analysis, among other procedures.

The comparison of each well's cumulative production history to original gas in place and remaining reserves (Fig. 1) (27215 bytes) indicated that well Olivarez 1 was underperforming. Accordingly, Olivarez 1 was analyzed in further detail. Several opportunities to improve production were identified.

Both Nodal analysis (Fig. 2) (14355 bytes) and production history matching (Fig. 3) (28748 bytes) indicated formation damage. A positive skin of 15.85 was causing the Olivarez 1 to under-perform. According to the post-frac production calculations, an optimized fracture stimulation would economically decrease the skin.

The review recommended that Merit fracture stimulate two existing zones in the Olivarez 1 well (Fig. 4) (34833 bytes). Five new gas zones, containing estimated reserves of 5.6 bcf, also were identified as future opportunities.

The recommended fracture treatment was optimized to yield the best return-on-investment (ROI) for Merit. The treatment, designed using a suite of fracture models, included a 500-ft fracture half-length with an average conductivity of 1,000 md-ft. Calculations showed this procedure would increase production more than five-fold, to 1 MMscfd from 175 Mcfd. Payout should occur within 30 days.

Merit, at first, chose to stimulate only one zone. A second would be stimulated if the initial zone proved successful.

After stimulating the first zone, from 9,275 to 9,304 ft (Fig. 4) (34833 bytes), gas production increased more than 1 MMcfd. A second zone, 9,000-9,092 ft, was subsequently stimulated, and its production also improved by more than 1 MMcfd.

Total gas production from the Olivarez 1 exceeded 2 MMcfd, surpassing the expected I MMcfd and nearing the original production from these two zones in 1981. Merit's investment was recovered within 28 days.

Both the successful stimulation of the Olivarez 1 and the remaining reservoir potential identified by the review of La Reforma field led Merit to initiate a 3D seismic survey over the area. The survey led to selecting eight new well locations that await drilling.

SINGLE WELL

In 1983, Global Natural Resources completed a 6-ft oil zone in the H. Braden 1 well located in Brazoria County, Tex. The well initially produced about 30 b/d of oil. As of April 1993, however, flow stopped.

Global investigated artificial lift, but found it to be uneconomical.

Joining Global, Schlumberger's production enhancement group explored other options for the well. This included a Nodal analysis of the currently completed zone to determine if stimulation would improve production. The review indicated stimulation would be uneconomical.

Next, the original open hole logs were reanalyzed in search of other nearby oil or gas pay zones. Several potential zones were identified; however, more specific reservoir details were needed.

A dual-burst thermal decay time logging run was recommended to and approved by Global. The log verified that sufficient hydrocarbons still remained in the potential zones and had not been produced by nearby wells. The new log data also verified whether the potential zones would produce oil or gas.

An elemental analysis program on the thermal decay time data (Fig. 5a) (36202 bytes) revealed an oil zone above and two gas zones below the current zone at 9,864-9,870 ft (Fig. 5b) (36202 bytes). These intervals are at 9,837-9,841 ft (oil), 9,9189,922 ft (gas), and 9,9279,931 ft (gas), respectively.

The production enhancement group believed that gas produced from the lowermost new zone would be sufficient to naturally lift the oil, flowing from both the original zone as well as the new oil zone. Thus, a recommendation was made to perforate the one new oil zone and the lowermost gas interval. The second gas interval would remain behind pipe until needed to combat pressure decline.

To suit the conditions present in the H. Braden 1, rigless, wire line perforating was recommended. This included using a 1- 11/16-in., through-tubing, strip-type gun system capable of discharging high-performance charges at six shots/ft.

Wellhead pressure control equipment allowed underbalanced perforating that would result in clean, productive perforations, while maintaining well control.

The procedures, including the performance review, the logging run, and the perforating job, were expected to payout within 16 days of initiating production. Global agreed to proceed.

After undergoing the specified perforation plan, the H. Braden 1 initially flowed 1 MMcfd of gas, lifting the oil with it, as expected. Production rates settled at 40 b/d of oil and 400 Mcfd of gas.

Global not only improved production levels from the H. Braden 1 while avoiding artificial lift, but also quickly recovered all project expenses. Actual project payout was within 9 days, beating expectations. Further, the newly acquired logging data and thorough analysis of all logs uncovered additional up-hole pay, which Global may consider for future enhancement work on the well.

ACKNOWLEDGMENTS

The authors thank Global Natural Resources and Merit Energy Co. for permission to publish their respective successful enhancement projects, as detailed here. Thanks also to Schlumberger for supporting this article.