Determination And Calculation Of Reasonable Drilling Fluid Density For Salt-gypsum Layers

Drilling in and through salt was for a long period avoided due to the challenges that happen to the oil and gas industry when drilling to these formations.However large oil and gas reservoirs are associated with salt structures.Some important oil and gas reservoirs are located below the salt bodies.To reach the hydrocarbons section is necessary to drill thick layers of salt with various features.The salt can reach considerable deformation when exposed to the drilling fluid.This deformation is a function of the magnitude of in-situ stresses,mud density,exposed time,temperature,and the mineralogical composition.This behavior is what is known as salt creep.Salt layers have its particularity and its creep property and these have serious implications on drilling engineering.Borehole necking and well bore instability due to salt creep are two major concerns in designing completions for production wells drilled through salt layers.Pressure changes that occur in the salt layers during drilling operation can cause borehole closure and instability.As such,predicting salt creep deformations is essential for designing completions for wells drilled through salt formations.In this paper a literature review of material models describing,the creep properties of the salt layers were investigated.Using an established material creep model,a finite element analysis(FEA)methodology using Abaqus is then presented for analyzing salt creep deformations.Also analysis of the mathematical model for salt rock creep and analysis of the steady-state creep law was done.According to the creep law of salt layer,I calculated the reasonable drilling fluid density when drilling the salt layers.Depending on examples,I create plate method for drilling fluid density,and make the calculation reasonable.