ABSTRACT

A comprehensive formation damage study was undertaken on selected fields in the Baram Delta acreage, offshore East Malaysia, to determine the extent and main causes of formation damage in the area. This was due to the high skin factor values interpreted from most transient well tests conducted throughout the years. A total of 70 gravel packed and 60 non-gravel packed wells (involving 220 completion zones) in 6 fields were covered in the study.

Based on statistical and pressure transient data analysis as well as an in-depth review of drilling and completion activities, it was found that the majority of non-gravel packed wells have low or negligible formation damage. Between 60 and 70% of the non-gravel packed wells have skin factors of less than 10. Most of these wells have constant skin factors as a function of time indicating that the damage, if any, did not increase with oil production.

On the other hand, the majority of gravel packed wells were damaged. As much as 70% of these wells have skin factors varying between 10 and 40. About half of these gravel packed wells have skin factors which increased with time indicating that the damage worsened with oil production. Formation damage in these gravel packed wells may be attributed to the gravel packing operations. This was further substantiated by well test results which showed that skin factors immediately alter perforating were essentially zero while those determined from pressure build-up tests carried out at a later date alter gravel packing operations were in the order of 10 to 100. It was also observed that although improvements in gravel packing and perforating practices were implemented through the years, no significant enhancement of flow efficiencies had resulted.

INTRODUCTION

Formation damage was suspected to be prevalent in the Baram Delta fields, offshore East Malaysia due to the high skin factor values interpreted from most transient well tests conducted throughout the years. A comprehensive formation damage study was therefore undertaken to determine the extent and main causes of formation damage in selected fields.

The Baram Delta fields are located between 10 and 30 km offshore Miri in the East Malaysian state of Sarawak (see Fig 1). This study covers the larger fields of Baram, Baronia, Betty, Bokor, Tukau, and West Lutong only, involving 70 gravel packed and 60 non-gravel packed wells (with a total of 220 completion zones). Two fields consist of only non-gravel packed wells, another two only gravel packed wells, and the remaining two contains a combination of both. This mix enabled a reasonably good basis for comparison.

Oil production from individual fields in the Baram Delta began between 1968 and 1982. Oil is found in sandstone reservoirs between the depths of 1900 and 9600 ft subsea. Oil viscosities vary between 0.2 to 1.0 cp. Initial solution gas-oil ratio ranges from 500 to 2000 scf/stb. The sands range from loosely consolidated to fine and well consolidated with no natural fractures. These reservoirs occur in stacks of several zones, each of which may or may not be distinctly separated from the others by shale columns. The reservoirs were interpreted to be deposited in deltaic to fluviomarine environments. They are normally pressured and usually have sizeable gas caps with medium to strong aquifer support. The oil column thickness ranges from tens of feet to 200 feet with porosity and permeability values of 9–29% and 10-several thousand millidarcies respectively.

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