Abstract

This paper describes the techniques and strategy implemented by ADMA-OPCO in acquiring a successful and cost-effective 3-D seismic survey in a highly congested field located offshore Abu Dhabi. The early planning of the survey, the team work, the adequate data QC and the interaction between the three phases of data acquisition, processing and interpretation are highlighted as the key elements which granted the success of this survey. They contributed in achieving the technical objectives and addressing efficiently the logistical issues in a cost-effective manner.

Introduction

The "F" field is a complex and congested Oil & Gas field located in offshore Abu Dhabi and operated by ADMA-OPCO. This field has been on production for more than thirty years and criss-crossed by a complex pattern of oil, gas and water injection pipelines as shown on Figure-1. These pipelines lie on the sea floor in water depths ranging from 38 ft. near the center of the field to 85 ft. at the edges. In addition, some 77 unmanned well head towers exist in the field area and are considered as obstructions for any seismic activity. These towers are linked to the "F" field Super Complex which is a production facility covering an area of approx. 500m by 300m and is located on the crest of the field (Figure-2).

The seismic data acquired in this field prior to the 3-D survey consisted of a total of six 2-D lines with only two lines crossing the crest part of the field (Figure-3).

The correlation of well log data revealed the presence of small faults affecting the Thamama reservoirs (Lower Cretaceous) with a few of them present in the deeper reservoirs of the Arab formation (Upper Jurassic).

These faults were also seen on the available 2-D seismic lines. However, due to the lack of adequate seismic coverage, it was not possible to produce an unambiguous interpretation of the fault throw and orientation (Figure-4).

In September, 1991 an interference test was carried out by ADMA-OPCO on the crestal part of the field in the Thamama reservoirs. The results showed that the reservoir was not homogeneous. In particular, it showed preferential transmissibility in a SouthWest-NorthEast direction.

Subsequently, ADMA-OPCO and the associated Shareholders decided in April, 1993 to acquire a 3-D Seismic Survey over the Thamama reservoirs of the "F" field.

The main technical objectives of this survey are:

  • To define as accurately as possible the fault pattern and positions especially in the crestal area of the field and which will affect the planned gas injection scheme.

  • If appropriate and possible, to be able to use the 3-D seismic data to characterize the Thamama reservoirs.

  • Correctly designed, it may be possible to use the 3-D seismic data to address the other deeper reservoirs.

This content is only available via PDF.
You can access this article if you purchase or spend a download.