New Approach and Innovative Technology Application in Complex and Mature Reservoirs - Achieving Ultimate Reserve Recovery and Economic Objectives for Huizhou Field, Offshore South China
Authors: Hong Lian Ji , Shi Huang Ying , Tran Thanh Binh , Scaruffi William , Zou Xiao Ping , Yao Pan , Xiang Tian , YanPing Li , Castellan Francisco Arturo , Brewster T. Wayne , Halomoan Parlindungan Monris , Bisain Amarjit Singh , Yang Liu 
Published: March 2015

Abstract
The Huizhou oil fields located offshore south China have been in production for 20 years. Since early 2007, a horizontal drilling campaign used conventional resistivity, gamma ray, and density-neutron logging-while-drilling (LWD) tools with a geosteering technique based on real-time images has been applied to recover bypassed reserves. Recent reservoir surveillance data and an updated model identified significant remaining thin oil column reserve in the reservoir's attic locations. As targets become thinner and more difficult to reach and stay within, accurate lateral placement of horizontal wells becomes crucial. Failing to reach and stay within sand targets would result in less reserve recovery and an uneconomic well. Advanced azimuthal LWD with the ability to map the distance to multiple key boundaries, including the water contact and the top and bottom of the reservoir structure in the remaining thin oil column, offers many advantages over conventional methods. Applying the technique has greatly enhanced the ability to geosteer, thus reaching complex reservoir targets and managing uncertainties by reducing errors that could lead to improper well placement.
Since the boundaries are detected and monitored in real time, any adjustment to the lateral trajectory is done gradually and accurately, thus optimizing lateral placement, minimizing drilling torque, and increasing the ability to drill farther for an extended-reach well.
Field operation examples from three challenging horizontal wells, including an extended-reach well, with different drilling and geological complexities demonstrate the value of the method. The examples show results of significantly higher production compared to the set targets, additional reserves, and recovery enhancement, as well as improvement in project economics.
The new approach and innovative azimuthal LWD technology implementation has proven its utility in achieving the ultimate objective of drilling horizontal wells in Huizhou oil fields. The application reduced the drilling cost, enabled reaching and staying within complex thin pay zones, and avoided unnecessary adjustments. Production from Huizhou fields has been increased and production decline rate has been reduced by 60% as the result of these successful wells. We believe this approach and technique could address other mature reservoirs development.

Introduction
The Huizhou oilfields block is located in the Pearl River basin approximately 200 km southeast of Hong Kong, South China Sea (Fig. 1). The block is commercially operated by CACT Operators Group, which consists of China National Offshore Oil Corporation (51%), Chevron (33%), and ENI (16%). Currently, there are total 8 platforms and 1 FPSO; which are producing oil and gas from 13 fields.