The Stability Technique Of Upper Formation In Algeria/ADRAR Oilfield

Algeria/ADRAR oilfield is a development project of OC-TOUAT(CNPC- SONATRACH). In this field,one French drilling team has drilled some wells in 1980s, but little document was preserved. Because of little geology and drilling documents, there are lots of accidents and complicate situations such as pipe sticking ,mud loss as well as borehole collapse and so on at the beginning of this project. All those increase the drilling cost and extent well construction time. So to resolve the stability of borehole in the long distance unconsolidated sand formation is the key to complete this project.The element to borehole stability include geologic factor (the physical characteristics and drill-ability of unconsolidated sandstone), artificial factor (every complexity occurring in well-site, include drilling parameter, drill fluid, hydraulics optimization, bottom hole pressure change during tripping, fluid column pressure change for the content of cuttings and so on ) and stress factor(when the formation is drilled, the stress of the borehole is changed, at the same time, the surrounding rock become instability too).The matter of hole instability seriously affect the drilling speed, drilling quality and costs. It especially lead to the new exploration area can't access to the formation of interest because of the hole instability. This also seriously affect exploratory progress and the synthetically economic benefit.In this paper, we find out the geologic factor, artificial factor, stress factor together with parameter optimize including drilling mud and drilling parameter which led the borehole instability in this field. Then, we analyze the mechanism and resolve means of mud loss and bridge plug which are the main forms of borehole instability in this field.In this paper we also combine the theory research with field experience. Researching about this theme can decrease the risk of construction in this great length unconsolidated sandstone and conglomerate formation, also can cut down the drilling time and can advance the economic benefit. So this paper not only has theory sense but also can guide the operation in drilling process.