Study On Drilling Fluid Technology For Complex Bituminous Formation

In the process of oil&gas development in the Middle East,highly heterogeneous and active bituminous formation were drilled frequently.It is difficult to predict the distribution effectively because of its irregular distribution.Active bitumen has the characteristics of plastic,creep-paste flow,strong viscosity temperature sensitivity and strong adhesion.It will seriously deteriorate the performance of drilling fluid after it invades the wellbore,and it is easy to cause complex problems such as screen paste and lost circulation,especially the prominent sticking problem,which is easy to cause forced sidetracking,completion of drilling ahead of schedule and even abandonment of wells have seriously affected drilling safety and caused huge economic losses..The technical problem of bituminous formation drilling fluid is a worldwide technical problem.Aiming at the technical difficulties of drilling fluids in bituminous formations,based on the analysis of different types of formation bitumen fabrics and physical and chemical characteristics,this paper clarifies the characteristics of formation bitumen intrusion under different influencing factors,reveals the influence of different types of bitumen and different intrusion levels on the performance of drilling fluids,and discusses the reasons for the sticking of bituminous formations,the technical countermeasures for the performance control of drilling fluids against formation bitumen pollution,the development of anti-formation bitumen pollution drilling fluid treatment agents,and the formation of complex bitumen formation drilling fluid technology.The heavy components of typical bitumen is high（>65%）,the content of trace elements（Fe,Ni,V,CA,etc.）is high,the microcracks and micropores are well developed,the cross section is metallic luster,and the characteristics of hardness and brittleness are obvious.Viscoelastic soft bitumen（softening point:80-140℃）has a high viscosity and strong viscosity temperature sensitivity.Under the bottom hole conditions,it will creep into the wellbore in a viscous flow state,which has a great impact on the density,rheological property,filtration and lubrication performance of drilling fluids,while hard bitumen（softening point:≥140℃）has very small influence on the drilling fluid performance.High viscosity and strong adhesion of active bitumen are the basic reasons for the deterioration of drilling fluid performance and pipe sticking.Focusing on viscoelastic soft bitumen,based on the basic principle of"graded collaborative control",the drilling fluid technology countermeasures for different bitumen invasion degree are proposed.In case of slight bitumen invasion（less than or equal to 5%）,bitumen emulsification and viscosity reduction method shall be preferred to emulsify and disperse bitumen in time to reduce the negative impact on drilling fluid performance;with the increase of bitumen invasion degree,bitumen curing method shall be adopted to timely and effectively solidify bitumen,so as to facilitate timely screening on the ground and prevent bitumen circulation.In case of serious bitumen invasion,the bitumen solidification plugging technical measures should be taken in time to effectively seal the bitumen invasion channel to slow or avoid continuous bitumen invasion,so as to provide guarantee for safe drilling through complex bituminous formation.In order to emulsify and disperse the bitumen invading the drilling fluid efficiently,the molecular structure of a new bis imidazoline quaternary ammonium salt emulsifier was optimized,and a novel octadecyl bis imidazoline quaternary ammonium salt emulsifier SDR-1 was developed,which has low critical micelle concentration,low foaming rate and good thermal stability,and good compatibility with drilling fluids in typical bituminous formations on site.The corrosion inhibition effect of SDR-1 is ideal.The SDR-1 can effectively emulsify and disperse the bitumen and reduce the viscosity of the drilling fluid with adding disel oil.The SDR-1 can effectively emulsify and disperse the bitumen and significantly reduce the viscosity of drilling fluid.SDR-1 can effectively reduce the surface tension of bitumen contaminated drilling fluid,and it is easy to adsorb and form film on the surface of bitumen particles,which can effectively inhibit the aggregation and growth of bitumen,and then exert the effect of emulsification and viscosity reduction.In view of the moderate invasion of bitumen,in order to strengthen the bitumen solidification and reduce adhesion,based on the principle of bitumen catalytic oxidation technology,a new composite bitumen curing agent GHJ-1 was prepared with matrix bitumen,metal catalytic oxidant Al₂O₃,Zn O and Fe Cl₃ as the main raw materials under the condition of blowing oxidation.The GHJ-1 has good compatibility with typical drilling fluids,and the optimal concentration is 2-4%.The GHJ-1 has complex solidification effect with bitumen,which can effectively increase the content of heavy components,improve the softening point,weaken the adhesion of bitumen,and facilitate the timely screening of the ground.In view of the severe invasion of bitumen,strengthening the bitumen solidification and reducing adhesion effect is closely combined with pressure sealing effect.With the cooperation of the GHJ-1 and pressure sealing materials,the solidification dense plugging formulas under different fracture opening conditions were obtained through experimental optimization,which can effectively improve the fracture sealing pressure bearing capacity（up to 8MPa）and effectively retard the bitumen invasion.Considering the invasion of bitumen and the influence of drilling fluid components such as bentonite content,lubricant and weighting materials,a set of drilling fluid formulation with excellent comprehensive performances was constructed,and the anti-bitumen ability was increased to 8-10%.In addition,based on the optimization experiments of releasing agents,stuck freeing spotting fluid SFS-1 was developed,which can effectively dissolve bitumen,destroy the structure of clay cake adhesion layer,and exhibits a short releasing time.