Abstract

A substantial reduction in field development cost has been realized by using high-angle, long-reach wells to develop the shallow Semangkok Field with only two (2) platforms. An estimated savings in initial development costs in the order of US$60M was realized over a three (3) platform development alternative based on more conventional directional wells. Conventional drilling equipment and methods were extended to new limits in drilling and completing wells with angles exceeding 70 to objective targets as shallow as 1250 m TVD-SS with departures exceeding 2000 m, The planning and drilling methods employed to successfully drill, survey, log, and complete these wells are presented in this paper. The cost deviations attributed to drilling at high inclinations amounted to less than 8% of the final well cost for 29 of 42 wells and two geologic sidetracks that were drilled at angles ranging from 60 to 75.

Introduction

Semangkok Field Location (Figure 1)

The Semangkok field is located 137 km east of Kuala Terengganu in the Malay Basin in the South China Sea at a water depth of 64 m, Its shallow oil reservoirs range from 1050 to 1380 m TVD-SS in depth and cover a relatively large area (about 7 km long and 3.7 km wide). The field development plan selected was based on a two (2) platform installation from which highly deviated wells were drilled to the mid and outer row objective targets.

Semangkok-A Platform

The Semangkok-A platform is a 5-module, 24-slot central processing platform fro. which concurrent drilling, producing, and gas compression operations were conducted. A self-contained platform rig was used for the drilling operations.

Semangkok-B Platform

The Semangkok-B platform is a 3-module, 18-slot satellite platform from which concurrent drilling and producing operations were conducted. A tender-assisted rig was used for the drilling operations.

Field Development Drilling

Conventional directional drilling equipment and methods were used to drill the highly deviated, long-reach wells. Curved drive pipe. and straight drive pipe. with deviated drive shoes were used to obtain the earliest possible kickoff points. Both jetting and mud motor/steering tool assemblies were used to build angle at rates of 3-5/30 m, depending on proximity of adjacent wells, formation drillability, and the respective target locations. Surveys were taken by conventional single shot and multishot survey tools. A 9 7/8" bladed type PDC bit was used extensively over the hold-angle portion of the 9 7/8" production holes. A low solids seawater-polymer -starch mud system was used to drill the surface and production holes. A standard combination logging production holes. A standard combination logging tool was used to log all of the wells except for three (3) wells with angles exceeding 72. These wells were logged with a thru-drillpipe slim hole tool. All wells were completed with wireline set permanent packers and conventional downhole permanent packers and conventional downhole completion assemblies equipped with side pocket mandrels for future installation of gas lift valves. All wireline completion work was performed with regular 0.092" wireline units. The wells were perforated underbalanced with a 2 1/8" thru-tubing perforated underbalanced with a 2 1/8" thru-tubing strip-jet gun. The presence of shallow gas sand: complicated the drilling program. Both conductor and surface casing strings were required. A normal formation pressure gradient exists thru the objective sands. Coal stringers are present at the objective sand tops which had a tendency to slough when initially drilled. The drilling practices that were employed to successfully drill, evaluate, and complete the highly deviated wells are presented herein. Steps taken to minimize stuck drill strings, maintain directional control, improve drilling efficiency, obtain open hole logs, and complete the wells are covered. Minimal problems were experienced that could be attributed to operating at the high angles in the long-reach wells. Only three (3) sidetracks were required to bypass stuck bottom hole assemblies. Standard logs were obtained in all but four (4) production holes. production holes.

FIELD DEVELOPMENT PLANS

3-Platform Case (Figure 2)

The initial field development plan considered wan based on drilling 40 wells fro. three (3) platforms. The plan called for drilling only sixteen (16) outer row directional wells to maximum inclinations of 55. The objective target locations of these wells fell within the range of 1050 to 1380 m TVD-SS vertical depth and from 1380 to 1490 m horizontal displacement.

2-Platform Case (Figure 3)

The final plan selected called for drilling 39 wells from two (2) platforms (21 wells in the north end of the field from the A-platform and 18 wells in the south end of the field from the B-platform). This plan required the drilling of highly deviated mid and outer row wells from both platforms in order to obtain the same well spacing coverage as the three (3) platform case. A total of 18 wells were planned for inclinations ranging from 60 to 71.5. planned for inclinations ranging from 60 to 71.5. 2-Platform Actual Field Development (Figures 4 and 5)

During actual development of the field, geological interpretation and mapping revisions were made to accommodate a fault remapping and discovery of new oil reserves in the lowermost reservoir which increased the number of high-angle outer row wells to be drilled. Twenty-four (24) wells were drilled and completed from the Semangkok-A platform. Eighteen (18) wells were drilled from the Semangkok-B platform of which seventeen (17) were completed and one (1) was plugged and abandoned as the objective sands were faulted out. Two (2) wells were sidetracked to new targets due to failure to encounter productive oil. Figure 5 shows the vertical depths and horizontal displacements of the objective target locations for the twenty-nine (29) wells and two (2) sidetracks that were drilled to angles ranging from 60 to 75.25 (12 wells reached 70 or more).

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