Common Pitfalls of Mini-frac Analysis Robert Hawkes, Director of Completion Technologies Pure Energy Services 1 SPE Calgary, Sept 6, 2012
What They Didn’t Tell You About G -function and log-log plots 2 SPE Calgary, Sept 6, 2012
Reappraisal of the G Time Concept in Mini-Frac Analysis (SPE 160169, Bachman et al) G -function Thank you Google Images Bachman 3 SPE Calgary, Sept 6, 2012
Pre- Frac Diagnostics…. …….are we wasting our time? Most of our Pitfalls are coming from conventional thinking. Closure Pressure Still needs a holistic approach ........and more work! Leak-off Behaviour Pressure diagnostics is interpretive and heavily influenced by your discipline. After Closure Analysis Be careful how you impose a flow regime on the data. 4 SPE Calgary, Sept 6, 2012
Diagnostic Approach o Step-up or Step-down (neither) o Low Rate or Treatment Rate? What's the objective o Interpretation Pitfalls ISIP Closure Identification Think again Flow Regime Identification Not as easy as it seems Specialized Plots o Completion Considerations Hz wellbore (toe), Open Hole, Cemented Liner, Packer Leaks, Fluid Choice..... 5 SPE Calgary, Sept 6, 2012
Source of Maybe Some Common Pitfalls Maybe not YES !! Maybe not sure No Maybe not 6 SPE Calgary, Sept 6, 2012
Fracture Flow Regimes from Cinco-Ley (1978) ( Static ) 7 SPE Calgary, Sept 6, 2012
Carter Leak-off Model ( Dynamic ) The idea behind Carter's 1D leakoff Fluid Loss coefficient Velocity • if a filter-cake wall is building up it will allow less fluid to pass through a unit area in unit time √𝑢 - 𝑢 0 • the reservoir itself can take less and less fluid if it has been exposed to inflow • Both of these phenomena can be roughly approximated as " square-root h time behavior " 8 SPE Calgary, Sept 6, 2012
Who Has Seen This Shape of G -Function Plot?? 9 SPE Calgary, Sept 6, 2012
Who Has Seen This Shape of G-Function Plot?? 10 SPE Calgary, Sept 6, 2012
Who Has Seen This Shape of G -Function Plot?? 11 SPE Calgary, Sept 6, 2012
Who Has Seen This Shape of G -Function Plot?? 12 SPE Calgary, Sept 6, 2012
Who Has Seen This Behaviour on the Log-log Plot?? 13 SPE Calgary, Sept 6, 2012
SPE 140136 (2011) Paper identifies 3/2 slope feature and gives some theory _______. 14 SPE Calgary, Sept 6, 2012
So What Does the Welltesting Community Have to Offer to Mini-frac analysis? 15 SPE Calgary, Sept 6, 2012
First Mini-frac Derivative Plot, ~1990, Dr. Ted. Leshchyshyn 16 SPE Calgary, Sept 6, 2012
Well Test Analysis Log-Log Derivative Term (Agarwal Equivalent Time) Uses radial equivalent time t er for derivative This is NOT the same as D t D D t t d ( P ) p t Log _ Derivative t D er er dt t t er p Versatile even when radial flow not present This is why it is a universal approach to all well test problems 17 SPE Calgary, Sept 6, 2012
Nolte G -Function Analysis Using the Nolte G Function construct the various plots Assume no closure and the G Function Solution runs on forever …… .. Fluid What do things look like? Loss Velocity √𝑢 - 𝑢 0 h 18 SPE Calgary, Sept 6, 2012
Nolte G Function 19 SPE Calgary, Sept 6, 2012
Nolte G Function P vs G Classic Nolte GdP/dG vs G behavior with no closure dP/dG vs G 20 SPE Calgary, Sept 6, 2012
Nolte G Function Square root-t plot shows a character change from early time to late time with a constant flow regime. 21 SPE Calgary, Sept 6, 2012
Nolte G Function Early Time Slope = 1 Late Time Slope = 0.5 Derivative is the logarithmic derivative of ∆t…… …conventional approach. Late Time slope = 0.5 is Carter leak-off, not the conventional linear flow. 22 SPE Calgary, Sept 6, 2012
Nolte G Function m = 1.5 Early Time Slope = 1 Late Time Slope = 1.5* * as identified in paper 140136 Derivative is the logarithmic derivative of Agarwal equivalent (radial) time or…… …standard well test derivative. m = 1.0 NO linear flow slope, not picked up in paper 140136. 23 SPE Calgary, Sept 6, 2012
Classic Linear Flow Solution Infinite acting linear flow Injection period - classic linear flow Shut-in period - classic linear flow Use superposition to compute fall-off response 24 SPE Calgary, Sept 6, 2012
Linear Flow 25 SPE Calgary, Sept 6, 2012
Linear Flow No closure - infinite acting linear flow The G-function plot does not give meaningful results as the character changes from early time to late time with the same flow regime. 26 SPE Calgary, Sept 6, 2012
Linear Flow No closure - infinite acting linear flow Square root-t plot also has a character change from early time to late time with the same flow regime. 27 SPE Calgary, Sept 6, 2012
Linear Flow Early Slope = 0.5 No closure - infinite acting linear flow Late Slope = -0.5 Intercept is not closure for the special case 0.5 to -0.5 slope but is instead an artifact of the plot. Delta Time 28 SPE Calgary, Sept 6, 2012
Linear Flow Early Time Slope = 0.5 Late Time Slope = 0.5 Agarwal Equivalent Time 29 SPE Calgary, Sept 6, 2012
Well Test Analysis Approach The welltest log-log pressure derivative is the best flow regime indicator in our arsenal Theory is very well established in traditional PTA Cinco-ley and Samaniego, 1981 You need to dust off those old and forgotten welltesters in your closet and exploit them in the mini-frac world. Welltest Log-log derivative: the time function is NOT dt of the flow period the time function is with respect to Agarwal equivalent time – te = tp*dt/(tp+dt) The Log- log derivatives in Barree’s paper SPE 107877 are all with respect to dt as far as we can tell. 30 SPE Calgary, Sept 6, 2012
Observations and Comments: 1. We need to do flow regime identification before picking closure pressures Standard well test log-log derivative plot is key Flow regime dependent plots 2. Do we need replacements for the Combination G Function plot? 3. We need to calculate the correct derivatives 4. Do we even need ACA plots ? Why not use standard well test plots to calculate properties ? 31 SPE Calgary, Sept 6, 2012
Classic Barree Case Jean Marie oil well example 32 SPE Calgary, Sept 6, 2012
33 SPE Calgary, Sept 6, 2012
34 SPE Calgary, Sept 6, 2012
Conventional Approach 35 SPE Calgary, Sept 6, 2012
Conventional Approach Barree log-log dt plot Pfoc = 8300 kPa 36 SPE Calgary, Sept 6, 2012
Conventional Approach PDL ?? Pfoc = 8400 kPa 37 SPE Calgary, Sept 6, 2012
Conventional Approach Pfoc = 8400 kPa 38 SPE Calgary, Sept 6, 2012
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