| With the development of social economy,the demand for oil and gas in the world has also been greatly increased.However,there are fewer and fewer easy-to-develop oil and gas reservoirs on the original land,which makes the exploration and development of oil and gas reservoirs have to develop in the direction of deep wells and ultra-deep wells.The subsequent problem is that with the increase of well depth,the fluid column pressure of drilling fluid will also increase,which will lead to the increase of rock strength at the bottom of the well,and make the rock change from brittleness to plasticity.This paper starts with this point and studies the influence of compaction effect under liquid column pressure on rock drillability,and then obtains the influence of compaction effect under liquid column pressure on drilling rate and the influence law of drilling rate,so as to improve the mechanical drilling rate.In order to study the influence law of Rate of penetration,this paper mainly studies from two aspects.On the one hand,the relationship between drilling rate and weight on bit is analyzed by studying and correcting the drilling rate equation of cone micro-bit.On the other hand,the compaction effect under different bottom hole conditions is studied by drillability experiments on cores with different saturated media,and then how the compaction effect is affected is studied.The influence of compaction effect on drilling rate can be obtained indirectly from rock drillability.In the process of studying the relationship between drilling pressure and drilling rate,this paper adopts the micro-drillability test method(using micro-drill bit to carry out drillability test).During the test,continuous drilling is carried out by changing the drilling pressure.Using micro-drillable experiment method to drill continuously with variable drilling pressure will bring about three problems:too thin through-hole wall,large number of core requirements,and the influence of bottom hole shape on the results.The method to solve the problem that the through hole wall is too thin is to improve the size of the cone micro-bit.To solve the problem of large number of core requirements,the shortest drilling distance is improved,The improved minimum drilling distance is tested and verified.The method to solve the influence of bottom hole shape is to take into account the influence of bottom hole shape and size on drilling pressure-drilling rate curve and optimize the drilling rate curve.Then,the drillability K is redefined as the volume of rock broken by breaking energy(breaking work)and a preliminary drilling rate equation is established.Then the actual data are fitted to get the real equation of drilling pressure and drilling rate.In the study of the influence of compaction effect on drilling rate,the compaction effect under different bottom hole conditions is studied,and three main compaction effects are obtained.Because strength and plastic brittleness are the factors affecting rock drillability,through compressive strength and stress-strain tests of rocks under different compaction effects,the influence of compaction effect on rock strength and plastic brittleness is obtained,and the influence of compaction effect on rock drillability is studied indirectly.Then the rock drillability extreme values under different cutting methods are studied,and the influence of cutting methods on compaction methods is obtained.Finally,the influence law of compaction effect on drilling rate is obtained.Through the above-mentioned research on drilling pressure and drilling rate,the equation of drilling pressure-drilling rate is obtained,which provides an effective method to study the relationship between drilling pressure and drilling rate.Through a series of studies on the influence of the compaction effect under the liquid column pressure on rock drillability,the influence of the liquid column pressure on drilling rate is indirectly obtained,which provides a certain entry point and new ideas for future research in this field. |
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