RIASSUNTO
Summary
ADMA-OPCO drilled its first deep Khuff well using various types of tooth and diamond bits at very high cost/ft. Through various trial runs, turbodrilling with diamond and polycrystalline bits proved to be most polycrystalline bits proved to be most efficient method to drill the 12 1/4 and 8 3/8 phases.
By using the right bit programme and reducing the sticking problems, a dramatic improvement in ROP and average cost/ft was achieved.
Introduction
Natural gas production commanded greater attention at the beginning of 1976 in the Emirate of Abu Dhabi. With the commissioning of the LNG plant, ADMA-OPCO took steps to explore for natural gas reserves around offshore Abu Dhabi in 1977.
The main area of investigation was the Permian Khuff formation which was found to Permian Khuff formation which was found to be gas-bearing in neighboring Gulf countries.
The drilling of Khuff wells in the Abu Dhabi Emirate (both onshore and offshore) was non-existent prior to ADMA-OPCO's first well. ADMA-OPCO's drilling was limited to sequences down to Izhara Formation depths. The original drilling data were sparse and regional, hence representing only best guesses.
It was also considered on regional grounds, that sole sequences to be penetrated were porous and could contain high pressured gas porous and could contain high pressured gas with large amounts of H2S. Thus they should be treated with caution when encountered.
Since then, ADMA-OPCO has successfully drilled 9 Khuff wells to a maximum depth of 17800 ft BRT.
As well as continually achieving worthwhile reductions in cost/ft by utilizing the right selection of bits, substantial savings have been made by eliminating the occurrence of struck pipe and consequent sidetracking.
The adoption of ADMA-OPCO's Khuff drilling guidelines by other operating companies within the Abu Dhabi Emirate reflects the success rate and cost effectiveness it has achieved.
GENERAL
- GEOLOGY
The 9 offshore Khuff wells so far drilled are located on the NE - SW trend. (figure 1). However these are all separate anticlinal structures.
The NE-SW X-section through the wells below Araej Formation is as shown in figure 2. For convenience purpose the distances between wells is not to scale. All wells penetrated similar stratigraphic successions and lithologies.
The formations however, tend to thicken towards the North East and are encountered deeper along the South best.
The type of lithologies encountered are predominantly limestones, dolomites diolomitic limestones and minor anhydrites. Frequent shaly layers are present in sequences above the Khuff Formation especially in the Sudair and the Gulailah formations.