Protection Principle Analysis And Applied Research On Drilling Fluid Using In Water Sensitive-Unconsolidated Formation

Water sensitive formation and unconsolidated formation are the complex formations whichoften appear separately during drilling. And it indicates that it is more often to work in watersensitive-unconsolidated formation which is composite of the two formations above inexploration, trenchless and other engineerings according to further analysis. The compositeformation is easy to occur bore accidents such as reducing and amplifying diameter, expanding,collapsing and so on. And construction period for a project will be delayed, the cost will increase,even the bore may be scrapped for the accidents.The author finds the formation stable elements according to the analysis of the watersensitive-unconsolidated formation. Then the author finds the drilling fluid capabilities needed inthis composite formation according to the elements, and designs the testing system for testing thedrilling fluid capabilities. Meanwhile, the drilling fluid material with high performance price ratiooptimizationally be selected to used in the projects according to the project realities finallyobtained preferable efforts.1. The equation of the stress distribution surrounding the bore is obtained according to theanalysis of the water sensitive-unconsolidated formation. The formation stable elements includeoverburden loadoσ_v, maximum horizontal stressσ_H1, minimum horizontal stressσ_H2, porepressure P_P, cohesive force C, angle of internal frictionψ, uniaxial tensile strengthσ_bt, staticPoisson ratio,μ_s and actual stress factorη, drilling fluid capabilities and drilling operation etc.2.It summarizes the drilling fluid capabilities need to fit for the watersensitive-unconsolidated formation according to the formation stable elements analysis, whichincludes, (1) Controlling the density of the drill fluid rationally. (2) Plugging crevice and highpermeability pore efficiently. (3) Preferable shearing dilution. (4) Improving film formingperfectly. (5) Decreasing filtration rate. (6) Improving the quality of the filter cake. (7) Enhancingviscosity which could be increasing binding power of drilling fluid. (8) Preferable capability oflubrication and anti-drag. (9) Enhancing rejection capability of drilling fluid. 3. Three testing systems for the drilling fluid capabilities are designed which include filmforming and hatching film testing; avalanche grade testing and flow resistance losing testing.Film forming and hatching film testing is launched by the available API filter press and theavalanche grade testing is launched by avalanche grade instrument. The new functions of theseinstruments have been developed and the evaluation criterion is established. The lubrication anddrag reduction testing of drilling fluid are evaluated in a new way using the flow resistance losinginstrument designed by self. The testing system is constructed by these three testing and thedilution sheafing testing above which control and evaluate the drilling fluid capabilities used towork in the water sensitive-unconsolidated formation. But, the instruments need to be improvedand standardized in principle, finally to be quantified.4. It has analysed and tested the representative fluid material in principle, and optimized thefluid compoundings according to the three projects. Each compound is successful. They all keepsthe drilling process safely and smoothly by protecting bore hole. Meanwhile, it has saved theproject cost and decreased construction period.(1) The project of the technique of protected borehole wall and sealing for coal field drillingin Zhu Ma Dian, He Nan. The geologic characteristic in this area is that the Tertiary andQuaternary system are salient, especially, the water sensitive fromation is loose and crushwhich will cause reducing and chambering. The fluid system of LG-CMC has well rejectioncapability, decreasing filtration and viscosity which can be against the accidents in the bore andkeep the drilling process safely and efficiency.(2) The trenchless project in 4th industry road of Wu Han and north 4th circle road of BeiJing. The formation of the former area is fluidal water sensitive formation which will beexpansion after hygroscope. As referring above, the fluid system of LG tetrad guards against theformation creep during the process of long distance and heavy-caliber trenchless pipelying, theresistance force is also decreased for its well lubrication and less accident.(3) The project of the technique of fluid research, design and supervision for CCSD-SK, thisarea is representative water sensitive-unconsolidated formation. The fluid systems of PAM andLG has separately used in primary project and second project. The PAM fluid system has been inthe role of rejecting expansion in mud shale and agglutinating protecting sandrock collapsing.But there is a disadvantage of PAM system which is it has bad incompatibility with otheradditives. So it is hard to adjust and compound PAM system with other systems to settle thequestions may appear in further drilling. The fluid system of LG has be using in the secondproject, from now on the effect is well. For the questions of salt infusion and weighting whichmay appear in further drilling step, it has obtained several kinds of LG fliud systems which cansatisfy the needs in drilling. Otherwise, it is nessessary to reach and improve the anti-temperatureand fungi-proofing capabilities of LG fluid system because there are many vegetable gelatinsmaterials in it.There are three innovations in this article.1. Generalizing and summarying the formation stable elements according to the stableanalysis of the water sensitive-unconsolidated formation. Consequently finds the chilling fluid capabilities it must have to work in this composite formation.2. Design a new experiment system for testing drilling fluid capabilities used in watersensitive-unconsolidated formation. The new functions of the original instruments have beendeveloped and a new instrument is made initiatively by self. A new evaluation criterion isestablished to observate the capabilities of the drilling fluid used in this composit formation froma different view.3. A few compoundings with high performance price ratio and well capabilities have beenoptimized and selected according to the work theory of the fluid additives, the evaluation methodof the fluid capabilities and the project realities in water sensitive-unconsolidated formation.Which has been used in some projects and successcd in avoiding bore accidents, decreasingproject period and saving cost.