Enhanced Horizontal Drilling in the Jasmine Field, Gulf of Thailand
Authors: Maeso Carlos Jeronimo , Watcharanatakul Rattana , Kienast Val , Platt Christopher J. , Oglesby Chris , Permanasari Dian , Yusuf Nora , Fareed Abdul , Fey Scott Patrick , Saidi Khaled 
Published: May 2016

Pearl Oil operates the Jasmine and Ban Yen fields which are located in block B5/27 offshore Gulf of Thailand. The fields comprise multiple stacked clastic reservoirs. Individual sand bodies are generally thin and have historically been targeted by vertical or slant wells. Recently a change has been implemented to drill a higher percentage of high angle and horizontal wells, particularly in the thin 50 sand targets. The combination of integrated multi-disciplinary teamwork and new LWD technology has successfully delivered the horizontal wells. Accurate placement of a horizontal well producer has a large impact on the subsequent production potential. In the test case, the C-16 well was drilled in a 6 foot vertical thickness sand layer. The sand contact in the horizontal section was 100%. To date the well has had a cumulative production of 300,000 barrels of oil with an expected recoverable oil of 455,500 bbls. Water cut after 15 months production is 7%. The successful result from the test well has opened the door for the development of multiple new targets from existing platforms. A series of horizontal wells have been drilled during 2010 and early 2011 utilising a variety of LWD formation evaluation technologies (including distance to boundary and formation pressure measurements).

When targets are thin, precision is required in both landing and drilling horizontally. Drilling is fast so high real-time data rates are required during all phases of drilling. During the landing phase, a near-bit multifunction LWD tool has been run. This allows early recognition of gas sands and fluid contacts and optimization of landing. In high risk wells the tool has been run without chemical nuclear sources, utilizing pulsed neutron measurements of porosity and sigma to identify the gas-oil contact. In the horizontal sections a deep reading distance to boundary tool allows detection of sand bodies and optimization of the length steered within individual sands. A strong collaborative effort between the involved parties has been instrumental in the success of the wells.

Introduction

The Gulf of Thailand contains a thick sequence of clastics. Pearl Energy operates the Jasmine and Ban Yen fields within the basin (Kienast et al). The fields are located on the northwest flank of the Pattani Basin in block B5/27 (figure 1). These fields contain multiple oil and gas charged sands. The reservoir sands occur in a stacked sequence within a broad SSE plunging anticlinal structure. Depositional environments are lacustrine in the lower reservoir levels and fluvial channels in the overlying sections. These include shoreface, stacked channels and individual channels environments which can show complex lateral and vertical variations. Stacked channel sequences are generally laterally extensive and are thicker sand bodies (of the order of 20 to 70 feet thick). Individual channels and lacustrine shoreface deposits are much thinner, with a range of thicknesses of 3 to 15 feet common for oil bearing sands. Oil reservoirs are present at multiple levels and different sands across the fields. The presence of normal faults further adds to the complexity. Major fault trends are NNW to SSE and NE to SW. These compartmentalize significant portions of the reservoir (figure 2). In addition the structural dips are locally affected.