A New Straight-Line Analysis Method for Estimating Fracture/ReservoirProperties Based on Dynamic Fluid-in-Place Calculations

摘要

Straight-line analysis(SLA)methods,which are a sub-group of model-based techniques used for rate-transient analysis(RTA),have proven to be immensely useful for evaluating unconventional reservoirs.Transient data can be analyzed using SLA methods to extract reservoir/hydraulic fracture information,while boundary-dominated flow data can be interpreted for fluid-in-place estimates.Because transient flowperiods may be extensive,it is also advantageous to evaluate the volume of hydrocarbons-in-place contactedover time to assist with reserves assessment.The new SLA method introduced herein enables reservoir/fracture properties and contacted fluid-in-place(CFIP)to be estimated from the same plot,which is anadvantage over traditional SLA techniques.The new SLA method utilizes the Agarwal(2010)approach for CFIP estimation,extended to variablerate/pressure data for low permeability(unconventional)reservoirs.A log-log plot of CFIP versus materialbalance time(for liquids)or material balance pseudo-time(for gas)is created,which typically exhibitspower-law behavior during transient flow,and reaches a constant value(original fluid-in-place,OFIP)during boundary-dominated flow.Although CFIP calculations do not assume a flow geometry,the SLAmethod requires this to extract reservoir/fracture information.Herein,transient linear flow is assumed,andused for the SLA method derivation,which allows the linear flow parameter(LFP)to be extracted from they-intercept(at material balance time or material balance pseudo-time= 1 day)of a straight-line fit throughtransient data.OFIP can also be obtained from the stabilization level of the CFIP plot.Validation of the new SLA method for an undersaturated oil case is performed through application tosynthetic data generated with an analytical model.Thenew SLA results in estimates of LFP and OFIP that arein excellent agreement with model input(within 2%).Further,the results are consistent with the traditionalSLA methods used to estimate LFP(e.g.the square-root of time plot)and OFIP(e.g.the flowing materialbalance plot).Practical application of the new SLA method is demonstrated using field cases and experimental data.Field cases studied include online oil production from a multi-fractured horizontal well(MFHW)completedin a tight oil reservoir,and flowback water production from a second MFHW,also completed in a tightoil reservoir.Experimental(gas)data generated using a recently-introduced RTA core analysis technique,were also analyzed using the new SLA method.In all cases,the new SLA method results are in excellentagreement with traditional SLA methods.The new SLA method introduced herein is an easy-to-apply,fully-analytical RTA technique that canbe used for both reservoir/fracture characterization and hydrocarbons-in-place assessment.This methodshould provide important,complementary information to traditionally-used methods,such as square-rootof time and flowing material balance plots,which are commonly used by reservoir engineers for evaluatingunconventional reservoirs.