Successful Drill Cuttings Reinjection (CRI) Case History With Multiple Producing Wells On A Subsea Template Utilizing Low Cost Natural Oil Based Mud
Authors: Reddoch J. , Taylor C. , Smith R. 
Published: December 2007

This paper covers the drill cuttings reinjection engineering and operating techniques utilized by British Gas and Apollo Services, on the three year Tunisian Miskar project off the coast of Sfax, Tunisia. At the time of this writing, the subsea template phase has been completed, which included the drilling and cuttings injection on the first 7 wells over a subsea template. A platform was installed in the last quarter of 1994 and the second drilling phase of this project began in March of 1995. Ten (10) wells have been drilled to date and the cuttings have been disposed of in four (4) wells annuluses. The last three (3) wells were drilled while producing seven (7) wells.

Environmental regulations prohibited the dumping of oil based mud in the sea. Thus, if British Gas wanted the high penetration rates and, limited hole problems achieved by utilizing low cost, natural oil based mud; then cuttings reinjection presented the cost effective alternative.

All waste, from 10 wells, has been successfully pumped down four of the annuli with great success. Insignificant downtime has been experienced due to the injection process, even at instantaneous penetration rates in excess of 200 meters per hour on 12 1/4 inch hole. The CRI contractor rigged up and operated, with one man per 12 hour tower, the cuttings transfer system, the cuttings grinding/slurrification system and the triplex pump cuttings injection system. Over 2000 meters of limestone/claystone was encountered in each well while drilling and injecting successfully, (in the frac mode), into an impermeable claystone formation.

Addressed in this paper are:Well Planning with information on multiple well template drilling producing, as it relates to cuttings reinjection.Injection well disposal design and planning, including multiple well casing points, for development drilling while producing.Requirements for surface equipment, personnel and commissioning.Field Results and Data with adjustments for unplanned events.Economics of CRI and natural oil base verses synthetic (psuedo) oil mud.Conclusions and recommendations for future work.

Introduction

The Miskar project is located 75 miles ESE of the coast of Sfax, Tunisia (Fig. 1) of Northern Africa. The Tunisian Government mandated zero discharge of oil. The targets required drilling directionally thru highly reactive formations. These formations are most economically drilled utilizing natural oil based muds. A significant savings was foreseen utilizing natural oil base mud with successful Cuttings Reinjection to drill the wells, as opposed to utilizing water base or synthetic (psuedo) oil mud.

The project called for drilling 11 or more directionally drilled wells over a 3 year period (Fig. 2) commencing in the 1st quarter 1993. The first 8 wells were drilled and temporarily plugged via a jackup over a template, while the platform, pipeline and onshore processing facilities were built. All of the wells utilized mud line suspension hanger systems. The platform was installed in the last quarter of 1994. A jack up rig was moved back onto the platform to tie back the first wells for production. As of the writing of this paper, tiebacks have been completed and simultaneous production and drilling operations are in progress.

To date, all liquids and cuttings have been disposed of with no discharge to the environment and/or plugging or breaching.

This paper is comprised of 7 sections.

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