Abstract

In recent years, Measurement While Drilling / Logging While Drilling, MWD/LWD, formation evaluation applications have evolved to a point where many applications usually reserved for wireline logging can now be utilized using LWD technology. The latest of such applications come from formation testing while drilling tools which offer an alternative to wireline-based formation testing. Formation pressure data obtained while drilling is useful for traditional applications such as fluid typing, fluid contacts, and reservoir connectivity/isolation determinationas well as for improved well control with real-time measurement of pore pressures.

This paper presents a case history from the Middle East where a new Formation Tester While Drilling (FTWD) tool has recently been run. The tool utilizes a probe and packer concept similar to conventional wireline formation testers. A packer and probe are extended to the formation, and a small sample chamber is used to pressure test the formation. To obtain a formation pressure, it is required to stop drilling for a minimal period. Experience has shown this time period to be typically less than the time required to make a connection.

Field data from Saudi Arabia will be presented, where the Formation Tester While Drilling (FTWD) tool was recently run. The toolÍs operation, response, and applications of the data obtained are discussed.

Introduction

A Formation Tester While Drilling (FTWD) tool was recently run in the 8-½ hole section of a newly drilled well to demonstrate the ability to take accurate and reliable pressure tests in the drilling environment. This test was performed in the Qatif Field, Saudi Arabia for Saudi Aramco. This was the first run using a FTWD tool in the Middle East.

The Qatif field is located in the Eastern Province of Saudi Arabia approximately 50 km north of Dhahran, Saudi Arabia, Figure 1.It is a doubly plunging anticline composed of north and south domes. The field is approximately 10km wide and 50km long (6.2 x 31 miles) and consists of seven oil-bearing reservoirs

In late 2001 Saudi Aramco began an aggressive redevelopment of the field. The field was initially discovered in 1945 and has been intermittently produced since then. The field was shut-in and mothballed in the early 1990s. The redevelopment plan calls for the production of 500,000 BOPD of Arabian light crude from three of the reservoirs. In excess of 130 horizontal wells will be drilled to produce the planned rate.

The Qatif field is particularly challenging in that much of the 50-km long field is within the city limits of Qatif and other surrounding towns. Developing fields close to population centers calls for drilling wells from drilling islands, far from population centers and consequently far from the desired target locations. Many of these wells will have target entries 2 to 5 km from the surface location. As an added complication, two of the three main reservoirs at Qatif have extensive tar mats near the oil-water contact. The tar mats effectively isolate the oil column from the aquifer, necessitating the drilling of water injection wells. These horizontal injection wells must be placed within a narrow oil column window above the tar mat to insure adequate injectivity and minimize any oil trapped behind the injectors.

Figure 1: Location map of the Qatif Field

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