South China Sea Extended Well Testing Program: Implementation and Results
Authors: Paces R.S. , DeFu Liu 
Published: October 2008

Amoco Production Company and Nan hai East Oil Corporation (NHEOC) faced an unusual set of challenges after the discovery of the Liu hua 11-1 Field offshore the People's Republic of China in 1,000 feet (305 m) of water. The discovery well indicated that significant reserve potential existed; however, a number of adverse conditions threatened development. In order to evaluate the commercial potential of the Liu hua discovery and to better define the risks of proceeding with a development project, an extensive appraisal program was undertaken. During the appraisal program, extended production tests were conducted on three wells with distinctly different wellbore geometries; vertical, slanted, and horizontal. The program resulted in a significant revision of the original reservoir description and performance predictions. This paper describes the appraisal program, including the innovative deepwater extended testing system and well performance results. The appraisal program has proven to be effective by quantifying future reservoir performance and by identifying the appropriate size development system.

INTRODUCTION

Amoco in partnership with NHEOC discovered the Liuhua 11-1 oil field in early 1987. The field is located offshore China about 120 miles (193 km) southeast of Hong Kong in the Pearl River Mouth Basin of the South China Sea. Water depths over the field are in excess of 1,000 feet (305 m). A map illustrating the field's location is provided in Figure 1.

The discovery well, LH 11-1-1A, encountered a productive carbonate. The well drillstem tested 1,320 BPD (210 m3/d) of 20.4 degree API gravity oil with a maximum pressure drawdown of only 52 psi (3.5 atmospheres). A second well was drilled in mid 1987to confirm the discovery. This well, LH 11-1-3, flowed 360 BPD (57 m3/ d) of 16.4 degree API gravity oil with a 77 psi (5.2 atmosphere) drawdown. The discovery and confirmation well indicated that significant reserve potential existed; however, an unusual set of challenges were faced in evaluating the field's development potential. In addition to deep water, frequent typhoons, and poor crude properties (high viscosity dead oil) the oil zone was underlain by a large, active aquifer which might result in rapid water coning. It was recognized that extremely poor oil water mobility ratios would make aquifer response critical to production performance. Therefore, in order to evaluate the risks of development, an extensive appraisal program was undertaken.

A production system was designed, installed, and operated over two weather seasons in order to allow extended well testing. The system included a semi-submersible drilling rig (modified for one well production) and a captive tanker or Floating Production Storage and Offloading (FPSO) vessel to process and store produced fluids. A flexible marine hose was used to route production to the FPSO.

Electric submersible pumps were utilized for artificial lift. An illustration of the extended test system is provided in Figure 2. As the appraisal program evolved, three additional wells were drilled on the structure and three extended tests were performed in wells of differing wellbore geometry; a vertical well, a slanted well (78 degrees) and a horizontal well with over 2,000 feet (700 m) of bore at 90 degrees.