Method Of Predicting Soil Mechanical Parameters In Shallow Formation While Jetting Process In Deepwater Drilling

The mechanical properties of shallow soils in deep water play an important role in drilling design and construction as well as later oil and gas development.Since it is difficult to collect soil samples from layers deeper than 10 meters below the sea floor,the acquisition of shallow soil mechanics,based on the variation of drilling parameters in the deepwater drilling process,is not only economical but also reliable.The lack of the soil mechanical parameters will influence on the conductor installation design,the conservative design will waste lot of material and time,the non-conservative design will bring the risk of conductor stabilization.In order to fill the blank of the lack of the deepwater shallow soil mechanical parameters and optimize the conductor installation design and jetting operation parameters,developing researches on finding a convenient and feasible way to measure the shallow soil mechanical parameters would be necessary and significant.Based on the water jet theory,this paper firstly analyzed the features of submerged water jet during conductor jetting process.Then,combined with the failure criterion of cohesive soil,the mechanism of the bit on the seabed soil in the jetting process were studied and the calculation model of minimum displacement of water jetting to break soil and the calculation model of bit to the bottom hole depth was established.The study shows that the displacement of the pump has influence on the mechanism of conductor jetting break.By field jetting simulation experiment,the conductor side friction resistance change rule of surrounding soils during installing surface conductors were analyzed.According to the conductor resistance recovery cave which based on the experiment data,the relationship between the conductor resistance recovery coefficient and the real-time conductor side resistance and the limit conductor side resistance were found,the relation model of real-time conductor side resistance changing with time were established.Based on the conductor jetting string mechanics and bit to bottom hole mechanics analysis,using the stratified calculation method,the calculation model of real-time conductor side resistance were established.By field simulating conductor jetting experiment,the accuracy of the calculation model of real-time conductor side resistance had verified.By conductor side resistance indoor experiment,the rule of the conductor side resistance in different soil and different depth were researched.To verify the accuracy of the calculation model,the conductor side resistance in sand and clay soil experiments was made.In the soil-sand conductor side resistance different depth experiment,the rule of resistance in different kind soil was found and on the point of the soil qualitative change,the conductor side resistance has 3-5 times changes and the difference gradually increase with the increase of depth.Based on the results of the experiments,the identify criterion of soil character though conductor side resistance changes were established.Though the study on the mechanism of bit on the bottom hole in the jetting process and the calculation model of real-time conductor side resistance and he identify criterion of soil character though conductor side resistance changes and the relation model of conductor limit side resistance and soil parameters,using the operation parameters while jetting and conductor side resistance coefficient to calculate the soil mechanical parameters,at the same time,the deep water shallow prediction model while jetting process was established.By the field jetting simulation experiment and the actual jetting operation data validate the method is feasible and accurate.