Design and Implementation of a Horizontal Injector Program for the Benchamas Waterflood - Gulf of Thailand

Abstract

The Benchamas Development in the Gulf of Thailand is an oil play in a predominantly gas-condensate region. This development is unique in that the operator has significant oil reserves of high pour-point crude in several zones. Some zones have gas caps; others don't. Column heights are variable. The project is being developed as a waterflood with horizontal and monobore producers and injectors. The initial phase of horizontal producers were completed with sand exclusion capability, consisting of multilayerd sintered screens. This has so far proved to be effective. The Benchamas Waterflood project is comprised of eight stacked, compartmentalized, sandstone reservoirs. These sandstones are fluvial channels and are discontinuous. The waterflood is designed to maintain oil viscosity and gas cap location to maximize recovery. The economic impact of this waterflood is estimated to increase the recovery from an estimated 12–18% (primary) to 25–35% (secondary) of the OOIP. During the design stage of the waterflood project, simulation indicated that some horizontal injector wells would be required to enable the required injection rates. Three horizontal injectors were therefore planned. The drilling, completion, and clean up of these wells presented the Benchamas Asset Team with a series of unique challenges. Rock mechanics analysis was conducted in the decision process to address the need or lack of need for sand control. Results will be discussed. Drilling fluid and flow back aspects of the wells were carefully examined in order to avoid some of the problems of horizontal injectors drilled in other parts of the world by the company. An extensive literature search revealed that the laboratory work required to adequately address the issues comprehensively had not been done. The company and the fluids vendor collaborated to conduct the laboratory tests that were required to determine the correct combination of fluids and clean up procedures necessary to successfully install these wells. This paper will highlight the unique design challenges presented to the Asset Team, discuss the efforts that were undertaken to address these challenges and the results, and present the field results of the drilling, completion, clean up, and final injection results. Introduction The Benchamas Field is one of several fields located in the B8/32 Concession in the Gulf of Thailand. The concession is located some 180 kilometers to the South of Rayong and some 80 kilometers east of Koh Samui (figure 1). The Benchamas Field was discovered in 1995 by the concession partnership with the Benchamas 1 well. The Benchamas Production License Agreement was issued in June 1997. The Benchamas field covers 411 sq. km. and operates with 3 wellhead platforms, a processing platform, a quarters platform, and an FSO (figures 2&3). Production was initiated in June 1999. Production capacity was 25000 bbls per day oil and 180 MMSCF per day sales gas. Capacity has been increased to 40,000 bbls per day. Plans are underway to increase liquid production capacity to 75000 bbls per day. The field is uncharacteristic in the Gulf of Thailand in that it has several sizable oil zones in this predominately gas region. The Oil Reservoirs are in the BWA and BWB platform areas. The third and southernmost platfrom, BWC, is primarily gas and condensate. The field consists of multiple stacked zones of Miocene age sediments. The depositional environment is fluvial braided river channels. The depositional environment has resulted in a very heterogeneous set of reservoir packages.