Drilling and Completion Challenges and Countermeasures in Kenkiyak Complex Sub-salt Oil Field Development

Abstract

Kenkiyak sub-salt oil field is situated in the eastern edge of Kenkiyak tectonic belt of the Pre-Caspian Basin located in the Western Kazakhstan. The structure is a typical dome short anticline with the Permian salt dome Valley bands at the core of it. Since the reservoirs of the oilfield are buried deep with high pressure and extremely complicated geological conditions, drilling is extremely difficult, which made the field one of the well-known regions in the former Soviet Union for its drilling difficulty. The main geological features are: the diagenesis of the upper Mesozoic stratigraphy are bad; the Konggu group under the Permian developed thick salt dome, with the biggest thickness at the main site of salt dome reaching 3200 m; the buried depth of Carboniferous reservoir is between 4300-4500 m; the pressure coefficient of Permian and Carboniferous are respectively as high as 1.79-1.84 and 1.90-1.94; the leakage and kicking usually happened in the same layer; the oil and gas are rather active. The above-mentioned geological and reservoir features led to the following main problems in drilling and completion operation: 1) Downhole complex situations happen frequently in the upper Mesozoic strata (easy to leak, easy to collapse and easy to bits balling etc.); the possibility of salt dissolution, hole shrinking, plastic flow of dome and salt recrystallization existing in Konggu group of Permian led to the risk of the wellbore collapse, pipe stuck, casing collapse, as well as the deterioration of drilling fluid performance.As of the end of 2008, CNPC had successfully drilled 55 producing wells, with the success rate of 100%. The average drilling cycle had been shortened from more than 700d of the former Soviet Union to about 180d of CNPC. Single well initial production had increased from the original more than 30 tons / day in former soviet union time to an average of 200 tons / day or more nowadays, in which many wells performed the initial output of 500m ^ 3 / d or more, one well with the initial daily output of 1000 tons. Casing simplification, rational drilling fluid system, the bits selection and the open hole completion Ways and salt are key factors of the sub-salt field with high yield.