Research on restoration and stimulation technology for damaged geothermal formations

Abstract:

With the large-scale implementation of deep geothermal resources exploration and development， deep drilling technology and geothermal reservoir protection and restoration are facing new challenges and problems. At present， almost all deep geothermal drilling projects are using circulation boring method of water-based drilling fluid，which caused the damage of geothermal reservoir. In terms of geothermal reservoir restoration there are no compulsory standard in China. As a result， after the completion of geothermal Wells， many of them enter into the depressurization or pumping test without standardized geothermal reservoir restoration， resulting in the wrong evaluation of geothermal resources and contract disputes. This paper is based on a large number of geothermal drilling engineering examples， combined with oil and gas reservoir reconstruction literature. The damage type， lithology， mineral composition of plugging and filling， restoration and stimulation mechanism of geothermal formation are studied.The test and engineering practice show that hydrochloric acid （HCl）， mud acid （HCl+HF） and supercritical carbon dioxide can dissolve， expel， displace and expand the blockage or fracture in geothermal reservoir， which is the basic method to restore geothermal reservoir and improve the reservoir ermeability.The single restoration method is not effective in practical application， and the “two-in-one” or “three-in-one” method should be adopted in combination with the mechanism and degree of formation damage. In view of the common problems at present， the basic methods of restoration and stimulation technology for different types of geothermal reservoirs are put forward， in addition， the restoration and reconstruction of geothermal reservoirs should be an important part （working procedure） for geothermal drilling engineering.

Key words:geothermal reservoir;hydrochloric acid;mud acid;supercritical carbon dioxide;restoration for damaged formations;stimulation