Abstract

The transition from completion to production often requires the well to be killed immediately after perforation is completed, thus exposing the formation to potentially damaging kill fluid. To obtain a perforation tunnel with maximum productivity, this transition requires an optimal cleanup and the removal of the perforation damages.

A new underbalanced oriented perforating technique has been successfully implemented in Algeria. It combines the use of a formation isolation valve (FIV) to keep damaging completion fluid off the formation immediately after perforation and a perforating technique that utilizes the dynamic underbalanced method, which cleans perforations with more efficiency than conventional static underbalanced perforating method. In addition, a passive gun-orienting system was used to optimize the perforating process and enhance the well's performance.

The new technique was applied in 2003 to horizontal Well-1, which was drilled by in the Tadrart sandstone formation of the Berkine basin. After successful results in this well, the operator adopted its use in 2005 for two additional wells, Well-2 and Well-3.

The paper describes the application of the new technique to three horizontal wells of the Berkine basin and the evaluation of the related productivity increase vs. the conventional perforating method.

Introduction

In 1981, the operator started its exploration activity in block 403 of Algeria. The area is located in the Berkin basin, on the Sahara platform and close to the Tunisian border as shown in Fig. 1.

In the same area, several important oil discoveries including Rhourde Messaoud, Bir Rebaa North, Bir Rebaa West, and Bir Rebaa South West were made between 1981 and 1995.

The geological features in this region are characterized by two main fault systems: one main fault system that runs parallel to the northeast-southwest El Bourma regional fault, and a second system having a northwest-southeast direction. These systems were probably generated during the Ercynian phase and were reactivated during the Mesozoic period to generate the actual structural setup.

The anticlinal oil-bearing structures in this area are elongated in a north-northeast-south-southwest direction and bounded toward the west and south by the two main normal fault systems.

Field-a was discovered in 1986 with evidence of hydrocarbons in the Tadrart sandstone formation (Lower Devonian/Gedinian), which is one of the main reservoirs of this field.

Field-ß was discovered in 2002. It is located in the western sector of block 403 at a distance of 25 km west from Field-a. In this area, the Tadrart formation underlies directly below the hercynian unconformity (Fig. 2), which confirms the progressive erosion of the Devonian stratigraphic succession towards the east-northeast direction.

The petrophysical characteristics of the Tadrart sandstone are good with porosity ranging between 12 to 16%; the permeability is in the order of 100–200 md. The reservoir properties are quite homogeneous over the field, thus providing optimum candidate wells for the initial evaluation of the new perforating technique.

Background

Well-0 was the discovery well of Field-ß. It was drilled as a vertical well and completed with a standard completion including a 3.5-in. production tubing and a 7-in. packer. Well-0 was perforated in static underbalanced conditions and tested at 334 standard cubic meters per day (Sm3/d).

In May 2003, the operator started the drilling phase of Well-1, located 800 m west from Well-0. The original objective of Well-1 was to appraise the field after the Well-0 discovery. The decision to drill Well-1 as a horizontal well at the top of reservoir was motivated by the possibility of obtaining a higher production rate than Well-0.

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