Study On Plugging Of Huanxi Heavy Oil Reservoir And Application Of Deplugging Technology

Reservoir plugging is an issue occurring during the whole process of drilling, completing, down-hole working and producing, which causes the production of fluid in the region near the well bore or leads the dropdown of injection ability, decreasing the permeability of the reservoir. For different reservoir, the structure, composition, content and distribution of the reservoir rock grains and the interstitial materials are different. The damage of reservoir is a combined process of internal and external cause. Huanxi heavy oil reservoir is a sand stone formation, with grain pores as the main storage space. With the increase of cycle number of steam huff and puff, the formation pressure decreases at a great degree, the temperature decreases, the crude oil degas, the metabolites of bacteria accumulates, causing the formation plugging of heavy hydrocarbons, salt scale, iron compounds and biological film, etc., leading to the great dropdown of production. The issue of formation plugging has become a serious problem that affecting the oil production. So, it has become the key point to study the plugging mechanism of heavy oil reservoir and the methods of deplugging to increase the productivity of oil well and to enhance the recovery during the middle and late stage of heavy oil reservoir development.Through the study of plugging mechanism of heavy oil reservoir, so as to find out the reasons causing the reservoir plugging, various deplugging methods are investigated according to different conditions. Then, corresponding method is applied facing different plugging condition. Mixed solid acids can effectively relieve the pollutions caused by resin, asphaltene, paraffin, oil sludge and bio-organic matter and part of the inorganic plugging. Under certain conditions of temperature, mixed solid acid can release out mud acid, which can realize deep acidizing. Mixed solid acid can complex the metal ions in the formation, preventing the occurrence of second secondary precipitation. Mixed solid acid can be used in the well needing formation dealing because of the high steam injection pressure caused by the high viscosity of heavy oil. Suitable acidizing procedure with mud acid can prevent the secondary precipitation, heightening the effect of acidizing. Addition of corrosion inhibitor and anti-clay-swelling agent can improve reduce the degree of corrosion of equipment and pipeline by acid. While, acidizing will damage the rock matrix at some degree. Hydraulic shock and chemical combined deplugging method can create micro fracture in the region near the well bore, which can relieve the formation plugging, enlarging the passage of oil stream. But this method is likely to cause sand production in the loosely cemented formation. As for pressure pulse deplugging method, there is no need to move pipe string, which is very convenient, but the pressure is low, affecting the effect in part of wells, and the operating parameters should be optimized to heighten the operation efficiency.As for the oil wells in Huanxi reservoir, because of its high viscosity of heavy oil and the steam injection condition, the type of formation plugging is mainly the plugging caused by resin, asphaltene, emulsion and inorganic sediments. Mixed solid acid can effectively relieve the formation pollutions caused by the organic matters of resin, asphaltene, paraffin, etc. and the inorganic deposits, can complex the metal ions in the formation, preventing the occurrence of second secondary precipitation, and it is compatible very well with the Huanxi heavy oil, so the technology of mixed solid acid is a deplugging measure of low-cost and high-efficiency.