Evolvement of Completion Methods in a High Pressure Fractured Carbonate Reservoir: A Case Study
Authors: Chen Peng , Wang Xi , Wang Xugang , Xin Junhe , Wei Yuxiang , Zhu Aijun , Wang Yanfeng 
Published: December 2007

The wells in the Kenkiak Under-Saltdome (KUS) oilfield in Kazakhstan are difficult to drill and complete due to the complicated geological conditions. Historically, among 42 wells which had been drilled in this area 40 wells were abandoned; only 2 wells are in production. The wells were completed by casing perforation, with low averaged daily rate of production 64 tons per well. After 1997, initially, wells were continuously completed by casing perforation, with averaged daily rate of production around 100 tons per well.

In order to enhance the productive rate of wells, two major measures have been taken. On the one hand, search high productive zones; on the other hand, alter the well completion method to meet the new requirement. Openhole completion was introduced for vertical wells in the beginning in the carbonate reservoir and the first trial met with success, daily rate of production was as high as up to 480 tons. Afterwards, the openhole completion method was used for other vertical and high-angle wells, averaged daily rate of production of 6 openhole completed wells are over 300 tons per well.

However, with the extension of exploration and development, another four wells completed by open hole were located along the cracked zones. When the wells were put into production, both inner and outer tubing were blocked, which resulted in 4 wells off production.

To prevent the wells from tubing blocked during putting into production, as well as to keep the high productivity of the wells, later wells that are not suitable for openhole completion have been completed by punched or slotted liners. The averaged daily rate of production of 8 wells completed by punched or slotted liners are also over 300 tons per well.

Introduction

In general, methods of completion in a carbonate reservoir can be classified into three categories:1,2,3

- Perforated completions, including casing perforations and liner perforations.

- Openhole completions.

- Slotted liner completions.

In the Middle East (Saudi Arabia and UAE), liner perforations were used in the deep Permian carbonate Khuff formation where containing H2S and CO2 in downhole fluids.4 In Nevada, both casing and openhole completions were very effective to typical fracture developed porous dolomite and carbonates.5 In Thailand, openhole completion was used leading to a major gas discovery.6In west Texas, a case study revealed that operators often had found many of the wells had severely underperformed as openhole completions. Changing from liner/openhole completions to cemented liner completions was the major change necessary to accomplish a positive step-change in better economic return.7

Historically, perforated completions were used in the KUS field with low production. Openhole completions were afterward employed to increase the productivity. As a result, the yield of oil wells obtained greatly increased. Unfortunately, a few wells with openhole completion incurred both inside and outside tubings blocked when put into production. Liner completions have been put to use for dealing with the problem and gained effective results.