Modeling Fluid Flow Through Single Fractures Using Experimental, Stochastic and Simulation Approaches Dicman Alfred Masters Division

TAMU Introduction A NFR with extensive fractures Poor ultimate recovery Glasscock Co Reagan CoUpton Co Midland Co Martin CoBorden Co Spraberry Trend Area Reserves 10B bbls Recovery < 10 %

TAMU Why study fracture flow?   Improve prediction of sweep in Naturally Fractured reservoirs   Improve modeling of tracer studies Shale

TAMU Knowledge of the nature and mechanics of flow through a fracture becomes critical. Starts from basic understanding of core studies. Getting the basics right!

TAMU Fractures as parallel plates Historical perspective Constant width

TAMU Fracture Model w Historical perspective Constant permeability fracture surface

TAMU Cubic Law of Fractures Historical perspective Aperture half width Fracture length

TAMU w Fractures cannot be assumed as parallel plates. Reality ?

TAMU Fractures cannot be assumed as parallel plates. Reality ? A real fracture surface is rough and tortuous.

TAMU Tracy (1980) Iwai (1976) Neuzil(1980) Witherspoon (1980) The flow through a fracture follows preferred paths because of the variation in fracture aperture. Issues

TAMU Tsang&Tsang(1988) Brown (1987) The friction associated with the rough fracture surface affects the flow performance. More issues

TAMU The story so far …   Effect of friction in fracture flow simulations     Aperture Width ?       Stochastic aperture simulations Experimental support  

TAMU 1. 1.How do we obtain fracture aperture width? 2. 2.How do we simulate flow through fractures effectively? The objective Application of water-resource research technology into petroleum engineering

TAMU The approach Experimental Analysis Aperture width, q m, q f Fracture simulation Simulation Aperture distribution Stochastic Analysis

TAMU Fracture simulation Simulation Aperture distribution Stochastic Analysis The approach Experimental Analysis Aperture width, Q m, Q f

TAMU Information from experiments? Fracture permeability Fracture aperture Matrix and fracture flow contributions How these properties change with overburden stress Motivation

TAMU In the past … Impermeable surface Sand grains Apertures measured physically Flow experiments

TAMU New perspective… 500 psi 1000 psi1500 psi To quantify the change in aperture with overburden pressure

TAMU kmkm Experimental setup CORE HOLDER Permeameter Accumulator Graduated Cylinder Pump Hydraulic jack Matrix L=4.98 Cm A=4.96 Cm 2 Core : Berea

TAMU Experimental setup k av CORE HOLDER Permeameter Accumulator Graduated Cylinder Pump Hydraulic jack Core : Berea Matrix L=4.98 Cm A=4.96 Cm 2 Fracture kmkm

TAMU Permeability Changes at Variable Overburden Pressure k av kmkm Overburden Pressure (Psia) Permeability (md) 400

TAMU Using weighted averaging Fracture aperture? w l The unknowns k f and w (1)

TAMU From parallel-plate assumption (2) Combine the two equations to derive aperture width, w Average aperture equation

TAMU Fracture aperture Increase in overburden pressure decreases aperture width Overburden Pressure (Psia) Fracture Aperture (cm) 5 cc/min 10 cc/min 15 cc/min 20 cc/min 5 cc/min 10 cc/min 15 cc/min 20 cc/min

TAMU Matrix flow rate Overburden Pressure (Psia) Matrix Flow Rate (cc/min) 5 cc/min 10 cc/min 15 cc/min 20 cc/min

TAMU Fracture flow rate Overburden Pressure (Psia) Fracture Flow Rate (cc/min) 5 cc/min 10 cc/min 15 cc/min 20 cc/min K m = 200 md K f = darcy

TAMU Experimental Analysis Aperture width, Q m, Q f Fracture simulation Simulation Aperture distribution Stochastic Analysis The approach

TAMU o oIs it possible to create an entire aperture distribution from a single value of mean aperture? o oFrom experimental analysis w apertureMotivation

TAMU Log-Normal Mean Log-Normal Deviation Variable ( Aperture ) Aperture distribution Apertures distributed log-normally

TAMU Generation of apertures Through a mean and a variance

TAMU Application? Smooth fracture surface

TAMU Slightly rough fracture surface Application?

TAMU Application? Highly rough surface fracture Larger Aperture Size

TAMU Creation of the aperture map Variogram Stochastic analysis Lag distance Co- variance Kriging

TAMU Aperture distribution map Outcome of Kriging 3D 2D

TAMU Comparison Not the real picture but effective Good enough?

TAMU Experimental Analysis Aperture width, Q m, Q f Aperture distribution Stochastic Analysis The approach Fracture simulation Simulation

TAMU Motivation Tackle the issue of surface roughness Match the experimental results, namely flow and pressure drop across the core

TAMU Surface roughness 2b e Louis (1974) defined a friction factor, f based on the relative roughness, D is the hydraulic diameter = 2 × 2b

TAMU Surface roughness 2b e He proposed that when > f =

TAMU Surface roughness 2b e Modified cubic law

TAMU Permeability modification of the fracture surface Without frictionWith friction Effect of friction? 400 darcy 350 darcy

TAMU   Simulator used : CMG   Single phase black oil simulation   Laboratory dimensions (4.9875” x 2.51”)   Refined model : 31x15x15 layers   Fracture properties is introduced in 8 th layer   Matrix porosity =   Matrix permeability = 296 md Simulation Parameters Example of flow through single fractureSimulation

TAMU Flow on a smooth fracture surface

TAMU Flow on the distributed fracture surface follows preferred flow paths

TAMU Results Observed Overburden Pressure, psia Pressure Drop, psia Parallel Plate Theory Simulated

TAMU Overburden Pressure (Psia ) Flow Rate (cc/min) fracture matrix Flow match Parallel Plate Theory

TAMU The new approach Overburden Pressure, psia Pressure Drop, psia Observed Simulated

TAMU Flow match Overburden Pressure, psia Flow Rate, cc/min fracture matrix The new approach

TAMU Limitation? No roughness or tortuosity effect

TAMU Applications Gravity Drainage Experiment

TAMU X-Ray Detector X-Ray Source Brine X-ray ct scan

TAMU Parallel-Plate Theory Applications Gravity-Drainage Experiment

TAMU Our Approach Applications

TAMU The new approach Gravity-Drainage Experiment SimulationX ray CT Scan

TAMU Conclusions How do we obtain fracture-aperture width ? Obtain value for average aperture width through effective design of experiments Overburden Pressure (Psia) Fracture Aperture (cm)

TAMU Distribute fracture apertures Consider effect of friction caused by rough fracture surfaces How do we simulate flow through fractures more effectively ? Conclusions

TAMU Tail of frequency distribution impacts flow performance Tortuosity dominates fracture flow at high overburden pressures What other factors affect flow through fractures? Conclusions

TAMU Improve prediction of sweep in naturally fractured reservoirs Improve modeling of tracer studies Why study rugosity in fractures? Conclusions