The Development Strategies for Gas Fields of Low Permeability, Low Abundance and in Heterogeneity
Authors: Ailin Jia , Dongbo He , Junwei Tang 
Published: December 2007

At present, production tight gas reservoirs with low permeability, low abundance and high heterogeneity is one of the main objects. Sulige gas field is one of the typical examples, having thin effective pay thickness, low production rate per well and poor production rate-maintenance. However, the total gas reserves are large, and important for PetroChina to economically develop this kind of gas reservoir.

Certain development strategies are proved to be effective for the development of this kind of reservoir. The principle of low cost should be insisted during the development process. At the same time, specific development modes including option of development block, progressive development, infilled well pattern should be adopted. In order to increase success rate of drilling, comprehensive studying should be adopted including geology, geophysics, and etc. Production rate per well should be allocated properly to maintain a relatively long period of stable production. Fracturing of separate layers and efficient production management are required to obtain a high cumulative gas production for a gas well. Surface equipment and underground equipment should be simplified, but within the safe limit, to cut cost. In addition, favorable gas price policy and innovative management benefit a lot to efficient development of this kind of gas reservoir.

At present, a type of sandbody gas reservoirs characterized by low permeability, low abundance and high heterogeneity are one of the main objects of tight gas development in China. The characters of low permeability and low pressure can bring up low gas deliverability. Although the area of gas field is large and total reserves are huge, the low abundance of the gas resource reduces its quality and development efficiency. The reservoir distribution is featured of high heterogeneity and small scale of effective sand as well as bad connectivity, and low single well probable reserves and their recovery. It is very difficult to develop this type of gas field, but as a kind of important gas resources, economical development is very important, especially when China is facing fast growth of gas market and lack of backup resources.

Sulige gas field is a typical example of the above type and holds the largest reserves in China. Since the Sulige gas field was discovered, many evaluation research works for the gas field development have been done. Firstly, many new technologies of high precision reservoir forecasting have been tested including 2d seismic, 3d seismic, multi-wave seismic, 3component 3D VSP, and etc, which distinctly improved data quality. Secondly, the new method for low pressure gas well capacity evaluation has been tested and found certain behaviors in the low pressure condition. Thirdly, some new drilling techniques have been applied, such as gas volume requirements for underbalanced drilling, slim-hole drilling, and so on, which promoted the drilling speed significantly. And then, as for gas production techniques, some technologies have been used such as fracturing of separate layers, commingling production, and differential pressure control, which increase the single well production and extend the stability production time. Finally, the experiments on gas gathering system have been developed, such as the technologies like simplified flow, low temperature dealkylation, and so on, reducing the cost of surface construction. Basing on above achievements, development strategies for this kind of gas field have basically been established.