Numerical simulation of hydraulic fracture propagation in weakly consolidated sandstone reservoirs

Frac-packing technology has been introduced to improve the development effect of weakly consolidated sandstone.It has double effects on increasing production and sand control.However,determining operation parameters of frac-packing is the key factor due to the particularity of weakly consolidated sandstone.In order to study the mechanisms of hydraulic fracture propagation and reveal the effect of fracturing parameters on fracture morphology in weakly consolidated sandstone,finite element numerical model of fluid-solid coupling is established to carry out numerical simulation to analyze influences of mechanical characteristics,formation permeability,fracturing fluid injection rate and viscosity on fracture propagation.The result shows that lower elastic modulus is favorable for inducing short and wide fractures and controls the fracture length while Poisson ratio has almost no effect.Large injection rate and high viscosity of fracturing fluid are advantageous to fracture initiation and propagation.Suitable fractures are produced when the injection rate is approximate to3–4m3/min and fluid viscosity is over100mPa?s.The leak-off of fracturing fluid to formation is rising with the increase of formation permeability,which is adverse to fracture propagation.The work provides theoretical reference to determine the construction parameters for the frac-packing design in weakly consolidated reservoirs.

A new method to optimize the fracture geometry of a frac-packed well in unconsolidated sandstone heavy oil reservoirs

The worldwide proven recoverable reserves of conventional oil are less than the amount of the heavy oil.Owing to weakly consolidated formation,sand production is an important problem encountered during oil production in heavy oil reservoirs,for which frac-pack technique is one of the most common treatments.Hence,how to obtain the optimal fracture geometry is the key to increasing well production and preventing sand.Due to the faultiness that current optimization of the fracture geometry only depends on well productivity,fracture-flow fraction was used to describe the contribution of the fracture collecting and conducting fluids from the reservoir.The higher the fracture-flow fraction,the more likely bilinear flow pattern occurs,thus leading to smaller flow resistance and better results in oil productivity and sand prevention.A reservoir numerical simulation model was established to simulate the long-term production dynamic of a fractured well in rectangular drainage areas.In order to reach the aim of increasing productivity meanwhile preventing sand,a new method based on Unified Fracture Design was developed to optimize the fracture geometry.For a specific reservoir and a certain amount of proppant injected to the target layer,there exits an optimal dimensionless fracture conductivity which corresponds to the maximum fracture-flow fraction,accordingly we can get the optimal fracture geometry.The formulas of the optimal fracture geometry were presented on square drainage area conditions,which are very convenient to apply.Equivalent Proppant Number was used to eliminate the impact of aspect ratios of rectangular drainage area,then,the same method to optimize the fracture geometry as mentioned for square drainage areas could be adopted too.

Comparison of lattice and pseudo 3D numerical simulation of tip screen out operation

Hydraulic fracturing(HF)is a commonly used technique to stimulate low permeability formations such as shale plays and tight formations.However,this method of well stimulation has also been used in high permeable unconsolidated sandstone formations to bypass near-wellbore formation damage and prevent sand production at some distance apart from the wellbore wall.The treatment is called frac-pack completion,where a short length but wide width fracture is formed by injecting aggressive concentrations of proppant into the fracture plane.This operation is known as tip screen-out(TSO).Detailed design of fluid and proppant,including an optimal pump schedule,is required to achieve satisfactory TSO.In this study,we first assess the lattice-based numerical method's capabilities for simulating hydraulic fracturing propagation in elastoplastic formation.The results will be compared with the same case simulation results using a pseudo 3D(P3D)model and analytical model.Second,we explore the Nolte(1986)design for frac-pack and TSO treatment using lattice-based software and the P3D model.The results showed that both models could simulate the hydraulic fracturing propagation in soft formation and TSO operation,while some differences were observed in generated geometry,the tip screenout time and net pressure profiles.The results are presented.It was noted that fracture propagation regime(viscosity/toughness),nonlocality and nonlinearity had an influence on the different geometries.The advantages of each model will be discussed.

Assessing the effect of well completion types on productivity in a class 1G gas hydrate reservoir under pseudo steady state

This work focuses on the assessment of the effect of well completion types on gas productivity in subsea gas hydrate reservoirs of class 1G type where the gas hydrates have decomposed into gas and water.Three types of vertical well completions are considered:frac-packed well with vertical hydraulic fracture;frac-packed well with horizontal hydraulic fracture,and a cased-hole gravel-packed well.Sensitivity analysis was conducted with analytical well inflow models to determine factors that affect the gas well productivity.The results of the analyses indicated that proppant mass pumped during fracture treatment slightly improves well productivity for frac-packed natural gas hydrate wells.Well productivity increases nonlinearly with fracture productivity up to a threshold value of 50,000 md for fracpacked well with horizontal fracture,above which further increase in fracture conductivity would create no benefit.With a proppant mass of 50,000 Ibm and a corresponding proppant volume of 504 ft3,commercial gas production rates of 14.9 MMscf/d,5.621 MMscf/d,and 11.35 MMscf/d are possible for frac-packed well with vertical fracture,frac-packed well with horizontal fracture,and cased-hole gravelpacked well,respectively.Because hydraulic fracture orientation depends on the in-situ formation stress,whether a well should be hydraulic-fractured or not depends on in-situ formation stress.