--> Abstract: Deep-Water Discoveries in Indonesia: An Integrated, Focused Exploration Success, by T. J. Brown, R. L. Shook, L. J. Edwards, and J. T. Noah; #90923 (1999)

Datapages, Inc.Print this page

BROWN, TREVOR J., REGGIE L. SHOOK, LESLIE J. EDWARDS, and JESSE T. NOAH, Unocal Indonesia Co.

Abstract: Deep-Water Discoveries in Indonesia: An Integrated, Focused Exploration Success

By utilizing an integrated, focused approach to exploration Unocal Indonesia has discovered a significant, deep-water petroleum province off the Mahakam Delta in Indonesia. The onshore/shelf area of the Kutei basin has been a hydrocarbon-producing province since 1897, containing an estimated 12 BBOE in ultimately recoverable reserves. The potential presence of a significant, deep-water petroleum system off the Mahakain Delta was long recognized by some and doubted by others. Doubts were held as to whether reservoir-quality sands or hydrocarbon source potential were present in the deep-water environment. Sparse 2D-seismic data coverage, a lack of well data and water depths extending to greater than 8000' made the prospect of deep-water exploratory drilling risky and expensive. Mobil's 1994 Perentis-1 well, the only deep-water well drilled in the Kutei basin to that date, was drilled in 1245' of water and discovered non-commercial gas in Middle Miocene sands.

Since 1969 Unocal Indonesia has explored for, and produced from, Upper Miocene, deltaic and shelf sediments derived from the Mahakam delta. In 1994 Unocal began questioning prevailing outer-shelf and deep-water geologic models due to the scarcity of well data upon which existing models were based. In 1995 an exploration 3D-seismic survey covering 880 km 2 was acquired over the outer-shelf/upper-slope area in Unocal's East Kalimantan Production Sharing Contract (PSC) area. The seismic data revealed features with the appearance of gas-bearing, upper-slope, channel sands indicating the potential presence of a deep-water petroleum system.

In April 1996 Unocal began a shallow-water, exploration drilling program based on an innovative philosophy known as "Saturation Exploration" or "SX". The SX philosophy arose from the recognition that an effective exploration drilling program should balance drilling risks and costs with geologic and geophysical risks and evaluation needs. By innovating and focusing on designing, drilling and evaluating wells appropriately many efficiency gains have been achieved.Average well costs and times have been significantly reduced when compared to wells drilled using a "conventional" exploration approach. In the first year of SX drilling 30 wells were drilled, mainly in water depths less than 1000', for an average cost of $1.52 MM. Since the discovery of a petroleum system on the upper slope the drilling system has been adapted to deep-water drilling.As of March 1999, 60 wells have been drilled in water depths ranging from 1000' to 4100' for an average cost of $3.60 MM.

A semi-submersible rig contracted on a long-term basis is used for SX drilling. Rig modifications enabling rapid drilling and rig-moves in the relatively calm environmental conditions prevalent in the Makassar Straits include a surface BOP stack, a pre-mooring system and a wireless, disposable guide-base. Many innovative, operational techniques increase the speed and efficiency with which wells are drilled and evaluated.

All SX wells are designed to be plugged and abandoned. Each well is designed by a cross-discipline team to ensure an appropriate balance is achieved between evaluating geological objectives, mitigating drilling hazards and minimizing well cost. 3D-seismic data, stacking velocity analysis and offset well data are used to assess potential drilling hazards and formation pressures. Casing design may be modified while the well is in progress if initial assessments.prove to be inaccurate. The program allows for some wells not to reach prognosed TD. Full evaluation of objective interval(s) has been achieved in nearly all SX wells drilled to date.

Prudent assessment of data needs minimizes the evaluation time and cost on each well. Maximizing the use of historical well data and extensive use of MDT (Modular Dynamics Formation Tester) data has optimized formation evaluation and reduced the need for Drill Stem Tests. Conventional cores have been cut as required to achieve specific evaluation objectives. Implementation of innovative wellsite practices has minimized the time spent wireline logging. The percentage of total well cost attributed to evaluation, including DST's, has been reduced to 13.4% from 30% measured in a "conventional" exploration program prior to SX.

Using a "portfolio" approach to economics and maximizing the number of well penetrations have increased the statistical opportunity of discovering economic hydrocarbon accumulations. The lower economic threshold achieved as a result of low well costs allows higher risk or smaller prospects to be drilled and a wider variety of play types to be tested.

Using the SX approach two significant, deep-water (2000'-3500' WD), Miocene oil and gas accumulations and numerous, smaller, Pliocene gas accumulations have been discovered and delineated since 1997. Development plans for these, the first deep-water fields in Indonesia, are under preparation whilst the exploration program, still in its infancy, moves to deeper waters.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England