Optimization And Innovation Works On Gas Gathering Technology And Techniques In The Sulige Gasfield

Abstract

Abstract: Compact lithologic gas reservoirs, with poor connectivity between the formations, complex geologic feature and unpredictable production layers, have been mostly discovered with strong heterogeneity in Sulige Gas Field, which is characterized by ‘Four Lows’, i.e. low pressure, low permeability, low production and low abundance. To solve these problems existing in this gas field, many tests and technical innovations have been made in the past 5 years to form the unique surface construction style of its own. This paper briefly introduces a series of new gathering technology and techniques adopted in the surface construction of Sulige Gas Field, i.e. downhole choking, no wellhead heating, no methanol feeding, concatenation of wells, measurement with liquids, medium/low-pressure gas gathering, normal-temperature separation, two-stage pressure boosting and centralized processing. Field experiences prove that the techniques mentioned above are fit for the development and construction of this gas field, thus providing helpful reference for the gas fields similar to Sulige Gas Field with ‘Four Lows’. 1. Geologic Feature of Sulige Gas Field and Difficulties in Development and Construction There are great difficulties in development and construction of Sulige Gas Field which is a typical low porosity, low permeability and compact natural gas reservoir with complex geologic feature and strong heterogeneity. In addition, there exists the problems of low production output, rapid pressure decline and unstable production performance, characterized by ‘For Lows’, i.e. low pressure, low permeability, low production and low abundance. The CH4 content in local gas is above 90% (volume fraction, similarity hereinafter), whereas H2S content is lower than 20mg/ m3 and CO2 content less than 3%. Apart from a certain quantity (2%-8%) of C2~C6, the gas also contains a small amount of C7+ heavy hydrocarbon, averagely 1×104m3 of gas producing about 0.02m3 of condensate per day, so it belongs to wet gas with low carbon-sulfur ratio and low condensate. On this account, it is an essential and urgent task to work out a set of self-owned surface gathering and transmission technology depending on the unique geologic feature of Sulige Gas Field by properly overcoming the following difficulties, mainly including:Low production of single wells, rapid pressure decline, unstable production performance, short life span of gas well, more wells required by unit production capacity, and harder investment control for surface construction.The producing pressure was as high as 22MPa in the earlier stage, but it declined rapidly. In most of the time gas production is under low pressure and it is difficult to determine system pressure.Gas wells have poor capacity of carrying liquid and wellhead temperature is low, resulting in frequent hydrate formation. If traditional methods against hydrate formation are used, methanol consumption will be great and the cost will increase.Both deoiling and dehydration are required because the gas stream contains a small amount of heavy hydrocarbon.