Study & Application Of High Density Drilling Fluid Technology

With expanding of oil & gas exploration and development region, oil drilling hasdeveloped gradually from shallow to deep, from inland to deserts, jungles, mountains, remoteareas, as well as overseas market with very complex formation. Drilling operations carried outin these areas is more difficult, low hour effectiveness and high cost, because of relativelydeep buried reservoir, large formation pressure changes, complex lithology. Specificindications are: in condition of deep/ultra high well, high underground temperature andpressure, complex strata, often drilling across high pressure gas formation, brine formationand gypsum mudstone; conventional drilling fluid system are difficult to resolve technicalproblems resulted from high solid content, high salinity filtrate, performance instability,excessive filtration and others; in the drilling process often occur downhole trouble such ascreep in salt gypsum layer and soft mudstone, hole instability, easy to blowout or lostcirculation, and blockage during tripping, and large hole size due to salt dissolution; abovetroubles seriously affect well bore quality, and create great difficulties for oil and gas drilling,hold oil and gas exploration process. To solve these troubles for normal drilling, and somewells need drilling fluid with densities as high as 2.50 3.00g/cm~3 , and good performance asa guarantee.In china, application of high density drilling fluid is relatively less, which the density ofonly in the range of 2.00 2.50g/cm~3, and application ultra high density drilling fluid, higherthan 2.50g/cm~3 even 3.00g/cm~3, report less. In duration of use of high density drilling fluid,there often occurred poor reheology, thick mud cake, high filtrate, high solid content and otherproblems, rheological properties difficult to maintain. The above problems made highexpectations on the drilling fluid technology, and thus to succeed in the exploration formationof such special development, must carry out research of abnormal high density drilling fluidwith density up to more than 2.50g/cm~3. In the paper, through a large number of experiments, developed formula of high densitydrilling fluid: 0.8% 1.5% bentonite slurry +0.1% 0.3% polymer +3% 5% filtrate reducer+6% 10% Thinner +3% 5% pH control agents +3 5% inorganic salts +1% 2% lubricant+0.2% HT stabilizer + active barite. It is showed that the fluid system has strong inhibitionand anti collapse capabilities, anti temperature and anti pollution resistant and goodlubrication, good rheological properties, good reservoir protection, return permeability≥85%.By now, the fluid system has been carried out in several wells. Application results show thatthe fluid system will accelerate the success of some oil and gas exploration with high pressure,improve drilling speed, shorten drilling cycle, reduce cost, enhance reservoir protection. Theresults are satisfactory, with good prospects for promotion and application, can create a goodeconomic and social benefits.