| Chang 6#oil bed in eastern Yanchang Qilicun oil field is the typical reservoir with ultra-low permeability and low porosity and short of natural driving energy from aquifer.Because the shallow depth of the reservoir,horizontal stratification of the horizontal thin interbedded sandstones and mudstones,the hydraulic fractures are horizontal and parallel with the formation.Moreover,due to multistage fracturing,there are more than one horizontal fractures through a wellbore.Because there is few such case with multi-layer horizontal fractures in the world,and the mechanism of the flow in it is very complex,how to develop this reservoir is still on the struggling stage:(1)for wells in the area where deletion is applied,oil production declines rapidly and the degree of the reservoir recovery is very low.(2)For other wells in some waterflooding area,water cut of the production wells usually increases rapidly and fast water breakthrough frequently happened to them even at a low water injection rate,which result in the poor oil production.Therefore,in this thesis,fluid flow in oil well with multiple horizontal fractures was investigated.Its production method and production characteristics were also studied.Fracture parameters are key to oil reservoir production strategy design,but in Qilicun oil field,only a few wells have been monitored and can provide the hydraulic fracture parameters.Hence in this thesis,considering both measurement accuracy and costs,the micro seismic monitoring,in-situ stress analysis,production analysis,well testing,well logging,production performance analysis were adopted to put forward an integrated method to distinguish the horizontal fractures.The integrated monitoring results show that,most of hydraulic fractures in the studied area are horizontal fractures.This paper research single phase flow,oil-water two phase flow,foam flooding,flow mechanism in horizontal well with multi-layer hydraulic fractures and its mathematical model were studied from the simple to complex research routine.1)For depletion performance of vertical well,a single-phase seepage mathematical model for multi-layer fractures was established based on the theory of Newman's product and Green's function.i.e.At first the source function of the ellipsoid in the infinite strata and the source functions of the vertical stripes are established.Then,the solutions,the pressure field,of the equations are obtained according to the arithmetic product of the two function.Based on the analytical solution,production equation was built considering the geometry of fractures(elliptical and sloping).and influencing factors on production,such as shape-factor,length and the interval of the hydraulic fractures,were discussed.The results show that the ratio of vertical to horizontal permeability affects the oil well productivity.If the area of the fractured faces are fixed,The production formula implies well production is higher if the ratio is closer to one.2).Proposed a new development mode of horizontal fracturing-arch-extended-reach-well to effectively develop the tight oil reservoir under the region of agricultural insurance,water source,the village.And its flow mechanism was researched.Using a bow well,the following problems can be settled:(1)compare to the vertical wells,its drill site is more flexible and can be set far from the above protected region so that the oil still can be exploited from the reservoir under that region.(2)compared to the normal horizontal well where usually only one horizontal fractures come into being,instead that only one layer of rocks contributes oil production to the well,arch-extended-reach-well pass through multiple formations and mainstage fracturing can generate multiple horizontal fractures and multiple oil layers can be exploited.The mechanism and characteristics of fluid flow in the reservoir divided into several flow unit,with horizontal fractured-horizontal wells are studied and its mathematic seepage model is deduced considering various size of the hydraulic fractures.The optimal schemes for development is put forward with regard to horizontal well shape,flow unit,interval spacing between two fractures,the vertical position of the horizontal fracture and inference between two fractures.The method is applied to in the oil field,and the result is remarkable.3)Because water injection is significant in local area,oil-water two phase flow equation in oil reservoir with multi-layer horizontal hydraulic fractures was set up.The well model was especially treated using global pressure,total flow velocity and JPVCM condition.Based on single phase production equation,oil-water two phase production equation in oil well with multi-layer horizontal hydraulic fractures was built.The equation is able to accurately calculate flow rate at abrupt interface of matrix-fracture,and can provide more accurate results compared with results from widely used SPU method.This equation was used for numerical simulation of oil reservoir with multi-layer horizontal hydraulic fractures by water injection development.In this way traditional Peaceman well model was replaced,and equation singularity caused by high conductivity discrete fractures was reduced.4)Mathematical model for foam flooding in oil reservoir with multi-layer horizontal hydraulic fractures was built to study feasibility of foam flooding in local area.This model presented the well model for horizontal wells with multi-layer horizontal hydraulic fractures and calculation method for oil,water and foam flow rate at abrupt interface of matrix-fracture.The concept of global pressure and connection condition at abrupt interface was expanded from two phases to three phases.And three phase flow rate equation of oil,water and foam(gas)at abrupt interface of matrix-fracture was strictly derived.Compared with widely used SPU method,this equation provides a more accurate result.5)The above-mentioned mathematical models considered stress deformation of fracture conductivity including reversible and irreversible changes.Then,using mathematical models,numerical simulation was conducted.Chang 6#production methods on including depletion production,water injection,gas injection,polymer injection,foam flooding,bow well with multi-layer horizontal hydraulic fractures were studied and compared.Main production parameters were optimized.And some conclusions were obtained:? When the certain well spacing is given,reasonable fracture half length is affected by the rate of vertical permeability to horizontal permeability.And fracture geometry can influence oil production.In the same area,production is higher when fracture approximates a circle;?The fracture conductivity model with stress and time effect is estabilished.Compared with fracture closure,the ineffective engry supply is the main reason for the rapid production decline;?The development mode of multi-horizontal seam-arch horizontal well is proposed,and the seepage model of multi-flow unit is established.The technique is applied to YanChang oilfield,and remarkable effect is obtained;?The mathematical model of oil-water two-phase seepage flow in the reservoir with multiple hydraulic horizontal fractures is established,and the well productivity formula is deduced and applied to numerical simulation as well model.It is worth recommending that the case two stage fractures in each flow unit is prior to other cases;?Experiments and numerical simulations show that foam flooding is generally more effective than conventional water injection methods. |
PDF Full Text Request