Abstract

The paper discusses the design. The field operations of drilling and completing a high productivity horizontal well in the Sirte basin of North Africa as well as the productive results obtained.

In Oct. - Nov. 1994. the Arabian Gulf Company (AGOCO) drilled, tested and put into production a horizontal well in the Elgiza formation (Eocene) of the An Nafurah field in the Sahara Desert. The main objectives were to increase the production rates and to alleviate water coning.

To update the existing information (the reservoir was considered partially depleted after over 14 years of production) a vertical pilot hole was drilled and logged, then plugged back, before kicking the well off.

After drilling the curve (medium radius) and turning the well horizon/al. a bottom hole assembly (BHA) twist-off occurred while the build section was being reamed. This resulted in a short "fish" in the hole at 78 ° angle. A fishing attempt with a hydraulic junk retriever proved unsuccessful and had to be followed by two sidetrack cement plugs The first one was a very typical case of "cement slip off' and had to be repeated with a different slurry' formulation and placement procedure. The lower part of the curve was successfully sidetracked from 52 °and re-drilled to 90 ° without incidents.

Running without difficulties to the end of the curve (EOC) and successfully cementing the stiff production casing (9 5 .8' diameter) despite the highly bent build section (actual BUR of 14 ° to 16 ° 30m were important achievements. This was mainly due to the special drilling fluid (an oil based inverted emulsion ype). a well-designed casing and cementing program, a skillful drilling crew.

A 1400ft. long horizontal lateral was drilled in three days' and left as an open hole completion. The well was flow tested on clean-up (at a very high rate) by using coiled tubing (CT) and small volumes of N2, At present, the well is flowing through a 12" choke.

The paper reviews the main steps in the design and field execution of this high productivity Saharan horizontal well focusing on some particular aspects of the field operations:

  • the fishing job at 78 ° angle in the curve;

  • the sidetrack operation from a high angle borehole;

  • re-drilling the lower section of the curve;

  • running a rigid 9 5 8" casing (without premium connections) through the high curvature build section;

  • an inexpensive technological package to minimize formation damage.

  • a special procedure to keep the horizontal lateral clean.

The technical and economic success of this horizontal project can be attributed to the "integrated technology approach" used throughout the entire project development.

Introduction

In Oct. - Nov 1994, AGOCO has drilled and completed a high productivity horizontal well in the Eigiza West reservoir well G I90H-51, Elgiza W Zone, NNU. The reservoir is located in the Nafurah Field of the Sirte Basin, in N. Sahara, about 450km south of the Mediterranean Coast, in the G.S.P.L.A.J.

Located in a mature field, with all twenty offsetting wells drilled and completed 14–15 years ago(the field was discovered over 18 years ago), the horizontal well had to answer several questions put forward by the Company:

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