The Research On Minimum Gas Influx Calculation In Gas Drilling Based On Absorption Characteristics Of Rock

Gas drilling has many advantages compared with other drilling methods, such asreducing reservoir damage, improving ROP, reducing the cost of operation, extending the lifeof drill bit and it is also good for environmental cleaning. The reasonable minimum gas influxcalculation in gas drilling is the key to ensure the success of gas drilling and formation waterproduction limits the application of it. In the circumstances of a certain amount of waterproduction and different water absorption, the transport medium of annular is different. Ifthere is the formation water in annular, it is easy to cause the problem of hole cleaning. It alsocan cause sticking which make gas drilling impossible in severe cases. Therefore the researchon minimum gas influx calculation in gas drilling based on absorption characteristics of rockhas a realistic significance.Basing on the absorption characteristics of rock, considering whether the formationwater is being absorbed, divide the flow situation of annulus fluid into gas-solid two-phaseflow and gas-liquid-solid three-phase flow, calculating minimum gas influx in gas drillingseparately for two cases.When the annulus fluid is gas-solid two-phase, adding the formation water quality to thedensity of cuttings by the water absorption of cuttings.The minimum gas influx in gas drillingbringing cuttings can be got. Getting minimum gas influx in gas drilling bringing cuttings andits water absorption is directly proportional relationship.When the annulus fluid is gas-liquid-solid three-phase, we consider the annulus fluidcarrying fluid in this paper. During the annulus fluid carrying fluid in gas drilling, gas-liquidsurface tension effects on droplet critical speed is larger, and the gas-liquid surface tension ismainly related with temperature of the gas-solid two-phase properties, this paper is based onthe theory of heat transfer, getting small droplet temperature downhole, determininggas-liquid surface tension of the temperature, and on the basis of the formation fluid brineconcentration again to modify gas-liquid surface tension, thus, getting the resulting criticalspeed of the gas with liquid carrying, getting minimum gas influx in both liquid and gasdrilling.According to the size of the energy and carrier of cuttings after absorbing water, choosethe bigger one to calculate minimum gas influx in gas drilling.