Technical Research On Completion Program Of Under-Salt Reservoir In Kenkiak Oilfield

In the Kenkiak Reservoir under the Salt Dome (KRUSD),with theapplication of the open-hole completion technology with triple casing,the drilling rate has been improved remarkably, the drilling cycle hasbeen reduced largely , the pay zones have been conserved in good condition,and the individual well output has been increased several times as well.but there are some tubing plugging troubles with 4 wells among the 10wells in which the technology has been applied, and the average outputhas been reduced seriously by these problems, therefore it is verynecessary to research the completion program of the wells in KRUSDthoroughly.This research started with analysis on formation pressure in KRUSD,then analyzed the earth stress and the compressive strength of thereservoir thoroughly. The pore pressure profiles in the reservoirs ofPermian and Carboniferous system have been analyzed respectively, theearth stress profiles and the compressive strength profiles inCarboniferous rocks have been established. This research provided afoundation for optimization about the well completion program.The Conclusions have been drawn after the data have been compared andanalyzed: there are 1-2 meters hard and fragile limestone with highstrength on the top of the Carboniferous, but about 7 meters softerlimestone under this formation with uniaxial strength 10-40MPa, so thisinterval is easier to collapse.The research on the extreme producing pressure differential has givencritical pressure differential values when a well is put into production,Combining the values with the uniaxial strength profiles that have beenestablished before, the extreme pressure differential profiles have beenfounded, and these values have made another foundation for producingprogram.For the above analyses and research on earth stress and extremepressure differential, the objective reasons for the tubing plugging havebe gotten. On the other hand, there are some unreasonable things on casingor tubing design to cause no way to clean cuttings from the borehole ,and it takes long time that pay zone soak in mud when the final open holecompletion is used. These are other reasons for tubing plugging. Afteradaptability evaluation on perforated hole, open hole and linercompletion, the reasonable measures about completion and production havebeen given. In all these completion programs, the liner completion is mostsuitable in KRUSD.An optimizing design on the liner and the combined string, and ageneral producing research has been carried out, and strengths of slottedliner and pre-perforated liner have been analyzed and checked. Athree-dimensional finite model has been established. On the help offinite-element-calculation software, the theory of elastic-plasticmechanics has been used to analyze stress distributions and collapseresistances of the two liners in several aspects, including on even load,on uneven load, and along different tracks. The qualitative relationsbetween collapse resistances of liner bodies and varied parameters havebeen given. This research has provided a foundation for design of the twoliners.The efforts of these researches have been used to test in 8 wells.In comparison with the well with open-hole completion, output 335.4t/d,each of the 8 wells with liner completion technology has average 333.9t/doutput. The researches have not only solved the tubing plugging problemin the open-hole completion well, but output of individual well has beenkept on a high and stable level with very remarkable economic benefit aswell.