Abstract: The volcanic rocks are buried in the depth of more than 3,500m in southern Songliao Basin, so the development effect by using vertical wells is not so satisfying. Through demonstration the method of using horizontal wells and the underbalanced drilling technique are decided to be used to realize high-efficiency development and better protect gas reservoirs. Unfavorable factors exist for Changshen horizontal well 1, such as high bottom hole temperature, long time of construction in the horizontal section, and difficult protection of sensitive gas reservoirs. Analysis shows that some problems may exist, such as wall instability and collapse, differential pressure of high-temperature drilling fluid, the pollution and damage of drilling fluid to gas reservoirs. Study is carried out including the high-temperature wall stabilization technique for deep underbalanced horizontal wells, the high-temperature rock-carrying lubrication technique, and the gas reservoir protecting technique. Good results are obtained through field application, and systematic high-temperature deep horizontal drilling techniques are developed, meeting the requirement of high-efficiency development of deep gas reservoirs.

Key words: southern Songliuao Basin, deep well, drilling fluid, underbalance, horizontal well