Study On Opening Conditions Of Fracture Of Carbonate Rock In Tahe Oilfield

Ordovician fracture-cavity reservoirs in Tahe Oilfield is rich in fractures,which play an important role in connecting caves and improving permeability.The early-stage depleted development of the reservoir reduces the pore pressure in fracture and leads to the closure of fractures,and result in fluid supply capacity.In the later-period exploration,the formation energy is maintained by water injection.As a result,the cracks open and are connected to the remote reservoir to increase the liquid supply capacity.However,there are many problems in the development of water injection in Tahe Oilfield,which have a lot to do with the opening and closing of cracks.In the process of waterflood development,it is also necessary to open or avoid reopening cracks that have been closed by controlling the pressure.At present,there are insufficient researches on the crack opening process,and it restricts the efficient water injection development in the Tahe Oilfield,and it is not conducive to the design of flow channels regulating agent and choice of the matching flow regulating agent.Therefore,it is significant to study the characteristics of the opening process of fractures in Tahe Oilfield Ordovician.This research summarizes the basic characteristics of Ordovician fracture-cavity reservoirs in the Tahe block by collecting previous reports and reviewing the literature,and combine drilling coring data and image logging data to determine fracture development intervals,statistics and analysis of crack occurrence parameters and other parameters.The fractures of the reservoir are mainly vertical seams and high angle seams,and the orientation of seams are mainly NW and NE fractures,and the density of cracks is low.Filling minerals are dominated by calcite and a few are filled with argillaceous and pyrite.Due to frequent filling,the cracks are poorly effective,and the features of the dissolved holes are obvious.Through experiments of crack opening and closing,the relationship between permeability and changes of effective stress during crack closing and opening is obtained.The experiment shows that the low-angle cracks are easier to be closed than the high-angle seams.Water injection is much efficient to open the cracks than the gas injection.Also the filling materials have an impediment to the closure of cracks.At the same time,by testing the influence of fluid pressure on crack opening under the constant of confining pressure,the relationship between fracture permeability and effective stress during crack opening is obtained,and the width of cracks during opening is predicted.Finally,based on the experimental results and considered the friction of water injection,we estimate the reasonable water injection pressure for crack opening,and clarify the change role of crack width in the process of opening to provide suggestions for the choice of sealing agent.