A NEW HOSTILE ENVIRONMENT WIRELINE FORMATION TESTING TOOL: A CASE STUDY FROM THE GULF OF THAILAND

摘要

Wireline formation testing in high-pressure and/or hightemperature (HPHT) wells has long been a challenge due to both the hostile operating environment and the general nature of formation testing. Acquiring numerous pressure measurements and extracting fluid samples can be a long process – and, in hot, deep, and small boreholes that are typical of HPHT wells, acquisition can be difficult. In the Gulf of Thailand (GoT), large-diameter formation testers had a history of sticking and needing fishing; and the high wellbore temperatures caused failures for tools across service companies. In this paper we describe a new wireline formation testing tool (WFT) designed specifically for hostile operating environments and present the results of over two years of field experience in Thailand. The Gulf of Thailand is a challenging area for obtaining log data primarily due to the hostile environmental conditions arising from the high geothermal temperature gradient coupled with the small-diameter, highly-deviated boreholes. The reservoirs typically contain gas due to the high temperature gradient, generally 2.5 deg F or more per 100 ft, and the relatively deep burial depths. Oil reservoirs are located to the north of the Pattani basin where temperature gradients are less. Extensive faulting and the discontinuous lenticular geometry of the sand reservoirs limit the areal size of accumulations. Across the basin, formation water is fresh (<5000 ppm equivalent NaCl) and the sands have a large variation of shale and silt levels. Such variation can make fluid identification from conventional log data difficult, particularly for the oil bearing reservoirs. Under these conditions, (1) formation testing for fluid identification using pressure gradients, (2) establishing well-to-well connectivity of pay sands, (3) sampling gas for per cent CO2 distribution, and (4) pressure profiling are of primary importance. This paper summarizes the field experience gained from over 300 wells logged with a new formation tester.