Research On Water Drilling Technology And Its Impact On Rock Of ZK212Well, Yangyi

Geothermal energy is a kind of valuable mineral resources come from the Earth,which is clean and renewable. Its development and utilization is becoming more andmore important. For the development of high-temperature geothermal resources,drilling technology is the key. Reasonable choice of drilling technology helps improveROP and reduce drilling costs.This paper relies on deep geothermal drilling project of production wells inYangyi, Tibet. This paper introduced the process of drilling wells of Yangyi zk212and studied its water drilling technology.For the difference between the pressure which impact ROP factors, this papercalculated formation pressure and annulus pressure of zk212, the results showed that:the formation pressure equivalent density increases with the depth, the change is inthe range of0.74~0.87g/cm3; annulus pressure equivalent density is slightly largerthan1.0g/cm3in the second section and the third second of the well. We alsoconducted a field test about leakage, analyzed the relationship between thetemperature and leakage of drilling fluid, also analyzed the relationship between theleakage and pressure. About the clear problem of cuttings, I think that drill hydraulicfactors did not play a role in cleaning the bottom cuttings. Annulus velocity is0.42m/sin the upper section and is0.81m/s in the lower section, so it had a good effect in thelower section than the upper section of the well. Finally, we analyzed the variation ofROP with depth, and we also analyzed the reasons for the variation.Thermal cracking phenomenon which is because of hot rocks encountered lowtemperature drilling fluid is another important reason which affected the ROP.High-temperature geothermal wells has a higher formation temperature than otherwells, the hot rocks produced temperature stress when the drilling fluid in contactwith the hot rocks during drilling. Rock strength and deformation will be changedunder the effect of temperature stress.The rocks with different temperatures will exhibit different properties aftercooling by water, so researching on physical and mechanical properties of the hot rocks after cooling by water has important theoretical and engineering significance. Inthis paper, I study the Granite. I processed18granite samples at first, then heated thesamples with different temperatures, additionally put them in cold water untilrecovered room temperature. Finally, the treated rock samples were measuredlongitudinal wave velocity and uniaxial compressive strength. After finishing theabove test, I analyzed the test results from the perspective of comparison. Accordingto the formation temperature conditions of Yangyi geothermal field, the results showthat longitudinal wave velocity decreased by about25%and elastic modulusdecreased by about20%and uniaxial compressive strength increased slightly after the200℃hot Granite was cooled.