Integrating Reservoir and Geomechanical Models to Compare the ...

SPE 16705

Integrating Reservoir and Geomechanical Models to Compare the Productivity of Shale Reservoirs Using Different Fracture Techniques S. Lakshminarayanan, R. Jayakumar, M. R. Safari, Jian Huang, R. Rai, S. Christian and U. Mutlu, Weatherford Hazim Abass, ARAMCO

Copyright 2013, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Unconventional Resources Conference and Exhibition -Asia Pacific held in Brisbane, Australia, 11–13 November 2013. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract mus t contain conspicuous acknowledgment of SPE copyright.

Abstract The ultra-tight nature of shale gas reservoirs has made hydraulic fracturing inevitable. Whilst most of the gas industry is driven by the success of hydraulic fracturing, alternate fracturing techniques have repeatedly been overlooked. In hydraulic fracturing, only 20-30% of the injected water is recovered during clean-up, and this causes a concern over the fracture efficiency. Additionally, the overbalanced pressure during fracturing poses a threat towards damaging the fracture sand face. A potential alternative to eliminate these drawbacks is a forgotten technology-pulsed gas fracturing. The pulsed fracturing (through high pressure gas) also makes the clean-up much faster/simpler. Although the stimulated reservoir volume (SRV) resulting from pulsed fracturing might not be comparable to the one resulting from hydraulic fracturing, it is suspected that the former technique would be more efficient especially in ductile shale where the industry lacks efficient stimulation technique as hydraulic fracturing fails to be successful. Hydraulic fracturing involves a relatively slow loading rate and this usually results in bi-wing fracture geometries. On the other hand, explosive fracturing involves very rapid loading of formation that can trigger multiple fractures. However, due to extreme stress/heat that is generated during the explosion, near wellbore region may reach the plastic limit which inhibits fracture growth away from the wellbore. The pulsed fracturing loading rate and peak load (via high energy gas or propellants) lies in between hydraulic and explosive fracturing processes. This technique has the potential to shatter ductile shale(s): in particular by triggering a ductile to brittle transition: at an optimized pulse rate at a certain depth. Through coupling of geomechanical and reservoir models, a workflow to predict the generated fracture networks and to quantify the productivity/efficiency of the same has been established. Additionally, in order to account for the various phenomena that are expected to occur during transient production, parameters such as desorption and stress dependent permeability have been considered and are presented in this paper. This paper serves as a platform to compare the models depicting the established process of hydraulic fracturing versus an alternate fracturing technique like pulsed gas fracturing.

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Introduction Nanodarcy rock has changed the entire face of the natural gas exploration business. In order to increase the extent of the SRV and produce reasonable amounts of gas, induced fracturing techniques (hydraulic fracturing, explosives, propellants etc.) have become unavoidable. Hydraulic fracturing is a popular option to enhance the SRV, and this operation typically produces one single fracture aligned with the maximum principal in-situ stress direction (Fig.1). Within the time/pressure scale of hydraulic fracturing operations, it is somewhat difficult to manipulate material properties (i.e. by utilizing rate/pressure dependency) and/or propagate multiple/branching fractures (e.g. that would help shatter rock and create self-propped fractures).

Fig. 1- Fracture patterns from various techniques (a) Hydraulic Fracturing (b) Explosive Fracturing (c) Pulsed Gas Fracturing

Explosives which usually have peak pressures with orders of magnitude above in-situ stresses often cause considerable crushing of the rock and leave a plastically deformed/compacted zone with locked in/residual compressive stresses. This process usually occurs in microseconds. Pulsed gas fracturing (as known as high energy gas fracturing, tailored pulse fracturing, propellant fracturing) creates a load about one order of magnitude higher than above the in-situ stress level but might stay below the plastic/compaction limit of the rock. Using this load, a ductile-brittle transition might be triggered with multiple fractures radiating away from the wellbore. This pressure load is applied in the order of milliseconds to create and extend multiple fractures radially from the borehole. The concept of pulsed fracturing is to customize the pressuretime behavior of a suitable propellant/gas to create multiple fractures and avoid limitations inherent in both 1 hydraulic and explosive fracturing . The generation of a fracture network/pattern through the simulation of an alternative fracturing technique allows us to couple the same with reservoir simulators and forecast production. Due to various limitations that exist while producing a reservoir that has been hydraulically fractured, production from a reservoir that has been fractured with gaseous media is expected to be highly beneficial. The elimination of the fracture face skin and the minimization of the clean up time are some of the key aspects that are anticipated through the employment of pulsed gas fracturing.

Geomechanical Analysis It is generally agreed that two types of loading operate on the surrounding rock during pulsed gas loading of a wellbore: (i) high strength stress wave or shock wave (dynamic loading) which arises out of combustion of the propellant in the wellbore and create initial fractures, and (ii) propellant gas seepage (quasi-static loading) into initial fractures which further promotes fracture opening and propagation. The dynamic and quasi-static loadings

SPE 167105

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are complementary to each other, the former initiate cracks around the borehole and the latter infiltrates gas into these cracks and causes further extension (if it is strong enough). Along these lines, after the application of the dynamic load, which creates multiple initial fractures, several post peak scenarios can be pursued. One scenario includes pumping of gas at a much reduced rate (compared to the dynamic loading process) into the initially created fracture network and for an extended amount of time. The type of loading and duration in this post-peak scenario is similar to hydraulic fracturing with respect to magnitude of injection pressure and duration.Throughout this paper and for simplicity, we will refer to this scenario as pulsedextended-gas fracturing (PEGF). To study effect of different stimulation scenarios on extent of fractures, a reservoir in Middle Brown gaseous shale 2 in Devonian formation, from Lincoln County, West Virginia was considered. It is assumed that the reservoir has 100 ft pay thickness, seated at 5000 ft, and is drilled with a vertical well. Numerical evaluation and geomechanical 1 analysis of this specific reservoir using an advanced geomechanical model was done by Safari et al .They found that for this specific reservoir, a pulse load with 250 MPa peak and 2000 MPa/ms increasing rate will create 5 biwing fractures (Fig.2). The length, orientation and extent of each fracture created after the initial pulse is shown in Fig.2. As shown in Fig.2, initial pulsed loading creates 5 bi-wing fractures with initial fracture lengths that vary between 20 to 30 ft. The aim of the following section is to quantify the post-peak extent due to gas penetration (i.e. after the initial pulse) using the technique (PEGF) described above. In the analysis we assume full symmetry (only 3 fractures will be simulated as shown and numbered in Fig.2) and simulate gas penetration into the existing network.

Fig. 2- Initial fractures geometry for a reservoir at 5000 ft. The dynamic load that was applies has 250 MPa peak and increase with 2000 MPa/ms

Analysis Results – Pulsed Extended Gas Fracturing (PEGF) It is presumed that fracturing fluids in this option is gelled-LPG and the proppant is effectively distributed after injection. It is assumed that the fluid carries out proppant with 10% volumetric concentration. The fracturing fluid is 3 injected 30 minutes at a rate of 10 bbl/min (total 50. bbl/min) into the initial network as shown in Fig.2. EFRAC3D is used to model PEGF stimulation which utilizes the initial length/geometry from Fig.3. The integrated geometry of all fractures after stimulation period is shown in Fig.3. Additionally, geometry and the width distribution of each fracture are shown in Fig.4, Fig.5, and Fig.6 individually, red color representing high fracture aperture while blue indicating lower end. According to Figs 3-6 gas loading of the initial network further extends fracture length (~ 350

4 6PE 167105 Frame 001  23 Jul 2013  EFRAC3D Output data

ft) and aperture (~ 0.25 inch max.). Note that fracture aperture vary with both length and height, due to the fluid pressure loss along both the horizontal and vertical axis during propagation. In this analysis, the difference between SHmin and SHmax is approximately 250 psi (almost isotropic). Therefore the fracture length, as well as the fracture aperture distribution, is similar for fractures in different orientations (i.e. after 30 minute injection and as shown in Fig. 3-6). Frame 001  23 Jul 2013  EFRAC3D Output data

Vertical wellbore

Z

True Vertical Depth (ft)

SH

X

5050

Frame5000 001  23 Jul 2013  EFRAC3D Output data -200 200

0 0

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5050

Frame 001  23 Jul 2013  EFRAC3D Output data

4950

Sh

Width (in): 0.02 0.06 0.1 0.14 0.18 0.22 0.26 0.3 True Vertical Depth (ft)

Width (in): 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.3 0.32 Low High Y Sv

X(

ft )

200

-200

5000

Time = 30.0815(mins) 10.0257(mins) 10.1099(mins) 10.2011(mins) 10.2924(mins) 10.3838(mins) 10.4744(mins) 10.5642(mins) 10.6591(mins) 10.7602(mins) 10.8501(mins) 10.9421(mins) 11.0357(mins) 11.1243(mins) 11.2109(mins) 11.3091(mins) 11.4020(mins) 11.4844(mins) 11.5741(mins) 11.6532(mins) 11.7305(mins) 11.8215(mins) 11.9193(mins) 12.0175(mins) 12.1156(mins) 12.2115(mins) 12.3065(mins) 12.4160(mins) 12.5137(mins) 12.6234(mins) 12.7253(mins) 12.8138(mins) 12.9090(mins) 13.0176(mins) 13.1181(mins) 13.2069(mins) 13.3031(mins) 13.4123(mins) 13.5111(mins) 13.6052(mins) 13.7081(mins) 13.7880(mins) 13.8747(mins) 13.9764(mins) 14.0639(mins) 14.1591(mins) 14.2684(mins) 14.3706(mins) 14.4610(mins) 14.5675(mins) 14.6931(mins) 14.8397(mins) 14.9790(mins) 15.0898(mins) 15.1802(mins) 15.2884(mins) 15.3770(mins) 15.4815(mins) 15.5834(mins) 15.7257(mins) 15.8344(mins) 15.9400(mins) 16.0624(mins) 16.1773(mins) 16.3302(mins) 16.4420(mins) 16.5519(mins) 16.6657(mins) 16.7584(mins) 16.8650(mins) 16.9771(mins) 17.1001(mins) 17.2130(mins) 17.3196(mins) 17.4212(mins) 17.5222(mins) 17.6210(mins) 17.7187(mins) 17.8314(mins) 17.9384(mins) 18.0484(mins) 18.1463(mins) 18.2647(mins) 18.3757(mins) 18.4818(mins) 18.5837(mins) 18.6655(mins) 18.7485(mins) 18.8338(mins) 18.9481(mins) 19.0334(mins) 19.1364(mins) 19.2190(mins) 19.2762(mins) 19.3407(mins) 19.4107(mins) 19.4853(mins) 19.5524(mins) 19.6426(mins) 19.7185(mins) 19.7974(mins) 19.8938(mins) 19.9764(mins) 20.0557(mins) 20.1375(mins) 20.2188(mins) 20.3006(mins) 20.3841(mins) 20.4677(mins) 20.5518(mins) 20.6355(mins) 20.7215(mins) 20.7938(mins) 20.8677(mins) 20.9461(mins) 21.0224(mins) 21.1022(mins) 21.1833(mins) 21.2854(mins) 21.3664(mins) 21.4466(mins) 21.5291(mins) 21.6147(mins) 21.6865(mins) 21.7676(mins) 21.8548(mins) 21.9473(mins) 22.0371(mins) 22.1277(mins) 22.2222(mins) 22.3157(mins) 22.4276(mins) 22.5535(mins) 22.6758(mins) 22.7946(mins) 22.8913(mins) 22.9858(mins) 23.0833(mins) 23.1982(mins) 23.3014(mins) 23.4023(mins) 23.5015(mins) 23.6020(mins) 23.7011(mins) 23.8010(mins) 23.8993(mins) 23.9677(mins) 24.0354(mins) 24.1063(mins) 24.2065(mins) 24.2701(mins) 24.3333(mins) 24.4205(mins) 24.4844(mins) 24.5542(mins) 24.6324(mins) 24.7078(mins) 24.7850(mins) 24.8639(mins) 24.9532(mins) 25.0355(mins) 25.1204(mins) 25.1962(mins) 25.2983(mins) 25.3779(mins) 25.4601(mins) 25.5428(mins) 25.6429(mins) 25.7277(mins) 25.8095(mins) 25.8926(mins) 25.9760(mins) 26.0598(mins) 26.1454(mins) 26.2309(mins) 26.3185(mins) 26.4062(mins) 26.4948(mins) 26.5846(mins) 26.6744(mins) 26.7648(mins) 26.8548(mins) 26.9474(mins) 27.0412(mins) 27.1321(mins) 27.2765(mins) 27.3694(mins) 27.4587(mins) 27.5480(mins) 27.6377(mins) 27.7400(mins) 27.8300(mins) 27.9163(mins) 28.0019(mins) 28.0872(mins) 28.1755(mins) 28.2617(mins) 28.3493(mins) 28.4867(mins) 28.5797(mins) 28.6851(mins) 28.7683(mins) 28.8578(mins) 28.9520(mins) 29.0683(mins) 29.1540(mins) 29.2440(mins) 29.3367(mins) 29.4331(mins) 29.5315(mins) 29.6338(mins) 29.7405(mins) 29.8513(mins) 29.9650(mins) 0.0080(mins) 0.0110(mins) 0.0124(mins) 0.0142(mins) 0.0163(mins) 0.0186(mins) 0.0212(mins) 0.0244(mins) 0.0280(mins) 0.0321(mins) 0.0367(mins) 0.0419(mins) 0.0477(mins) 0.0542(mins) 0.0614(mins) 0.0693(mins) 0.0778(mins) 0.0872(mins) 0.0972(mins) 0.1081(mins) 0.1197(mins) 0.1322(mins) 0.1454(mins) 0.1596(mins) 0.1745(mins) 0.1903(mins) 0.2065(mins) 0.2249(mins) 0.2434(mins) 0.2634(mins) 0.2836(mins) 0.3044(mins) 0.3257(mins) 0.3477(mins) 0.3709(mins) 0.3945(mins) 0.4192(mins) 0.4451(mins) 0.4715(mins) 0.4990(mins) 0.5274(mins) 0.5573(mins) 0.5886(mins) 0.6200(mins) 0.6530(mins) 0.6869(mins) 0.7225(mins) 0.7571(mins) 0.7936(mins) 0.8289(mins) 0.8649(mins) 0.9017(mins) 0.9416(mins) 0.9795(mins) 1.0191(mins) 1.0626(mins) 1.1056(mins) 1.1491(mins) 1.1970(mins) 1.2404(mins) 1.2845(mins) 1.3311(mins) 1.3757(mins) 1.4272(mins) 1.4745(mins) 1.5200(mins) 1.5667(mins) 1.6144(mins) 1.6657(mins) 1.7132(mins) 1.7624(mins) 1.8112(mins) 1.8618(mins) 1.9118(mins) 1.9639(mins) 2.0153(mins) 2.0679(mins) 2.1252(mins) 2.1737(mins) 2.2299(mins) 2.2878(mins) 2.3452(mins) 2.3967(mins) 2.4565(mins) 2.5146(mins) 2.5700(mins) 2.6317(mins) 2.6956(mins) 2.7533(mins) 2.8089(mins) 2.8668(mins) 2.9311(mins) 2.9888(mins) 3.0491(mins) 3.1080(mins) 3.1743(mins) 3.2330(mins) 3.2997(mins) 3.3637(mins) 3.4233(mins) 3.4886(mins) 3.5491(mins) 3.6079(mins) 3.6773(mins) 3.7435(mins) 3.8136(mins) 3.8807(mins) 3.9524(mins) 4.0201(mins) 4.0956(mins) 4.1597(mins) 4.2265(mins) 4.2924(mins) 4.3620(mins) 4.4277(mins) 4.5017(mins) 4.5779(mins) 4.6482(mins) 4.7177(mins) 4.7841(mins) 4.8611(mins) 4.9345(mins) 5.0140(mins) 5.0895(mins) 5.1498(mins) 5.2177(mins) 5.2923(mins) 5.3639(mins) 5.4279(mins) 5.5154(mins) 5.5874(mins) 5.6558(mins) 5.7269(mins) 5.8038(mins) 5.8781(mins) 5.9491(mins) 6.0358(mins) 6.1157(mins) 6.1918(mins) 6.2656(mins) 6.3410(mins) 6.4153(mins) 6.4919(mins) 6.5708(mins) 6.6548(mins) 6.7349(mins) 6.8223(mins) 6.9051(mins) 6.9941(mins) 7.0748(mins) 7.1563(mins) 7.2355(mins) 7.3081(mins) 7.3850(mins) 7.4555(mins) 7.5403(mins) 7.6199(mins) 7.7140(mins) 7.7939(mins) 7.8693(mins) 7.9552(mins) 8.0470(mins) 8.1362(mins) 8.2228(mins) 8.3056(mins) 8.3984(mins) 8.4813(mins) 8.5706(mins) 8.6582(mins) 8.7425(mins) 8.8304(mins) 8.9282(mins) 9.0186(mins) 9.1198(mins) 9.2046(mins) 9.2881(mins) 9.3651(mins) 9.4593(mins) 9.5340(mins) 9.6310(mins) 9.7188(mins) 9.8050(mins) 9.9176(mins) Injection Volume = 336.3075(barrels) 337.6355(barrels) 100.8811(barrels) 102.0166(barrels) 102.9678(barrels) 103.9015(barrels) 104.7617(barrels) 105.8186(barrels) 106.6670(barrels) 107.7439(barrels) 108.7246(barrels) 109.6883(barrels) 110.9505(barrels) 112.1609(barrels) 113.1017(barrels) 114.1206(barrels) 115.1382(barrels) 116.1580(barrels) 117.1674(barrels) 118.1689(barrels) 119.2100(barrels) 120.3255(barrels) 121.3291(barrels) 122.3590(barrels) 123.3637(barrels) 124.3668(barrels) 125.3330(barrels) 126.4443(barrels) 127.4954(barrels) 128.4267(barrels) 129.4391(barrels) 130.3305(barrels) 131.1892(barrels) 132.2095(barrels) 133.2560(barrels) 134.3433(barrels) 135.4323(barrels) 136.5025(barrels) 137.5620(barrels) 138.7869(barrels) 139.8748(barrels) 141.1045(barrels) 142.2486(barrels) 143.2411(barrels) 144.3084(barrels) 145.5266(barrels) 146.6535(barrels) 147.6472(barrels) 148.7244(barrels) 149.9483(barrels) 151.0786(barrels) 152.1130(barrels) 153.2896(barrels) 154.1697(barrels) 155.1475(barrels) 156.2958(barrels) 157.2836(barrels) 158.3581(barrels) 159.5931(barrels) 160.7475(barrels) 161.8146(barrels) 162.9929(barrels) 164.3713(barrels) 166.0289(barrels) 167.6037(barrels) 168.8534(barrels) 169.8659(barrels) 171.0774(barrels) 172.0646(barrels) 173.2333(barrels) 174.3707(barrels) 175.9670(barrels) 177.1861(barrels) 178.3700(barrels) 179.7409(barrels) 181.0280(barrels) 182.7442(barrels) 184.0051(barrels) 185.2414(barrels) 186.5079(barrels) 187.5284(barrels) 188.7236(barrels) 189.9797(barrels) 191.3536(barrels) 192.6218(barrels) 193.8229(barrels) 194.9641(barrels) 196.0987(barrels) 197.2080(barrels) 198.3044(barrels) 199.5694(barrels) 200.7689(barrels) 201.9915(barrels) 203.0875(barrels) 204.4146(barrels) 205.6597(barrels) 206.8480(barrels) 207.9880(barrels) 208.8973(barrels) 209.8211(barrels) 210.7696(barrels) 212.0813(barrels) 213.0131(barrels) 214.1417(barrels) 215.0533(barrels) 215.6788(barrels) 216.3937(barrels) 217.1667(barrels) 217.9931(barrels) 218.7317(barrels) 219.7302(barrels) 220.5614(barrels) 221.4378(barrels) 222.5148(barrels) 223.4351(barrels) 224.3254(barrels) 225.2495(barrels) 226.1653(barrels) 227.0888(barrels) 228.0315(barrels) 228.9754(barrels) 229.9249(barrels) 230.8672(barrels) 231.8393(barrels) 232.6523(barrels) 233.4828(barrels) 234.3660(barrels) 235.2236(barrels) 236.1216(barrels) 237.0353(barrels) 238.2079(barrels) 239.1100(barrels) 240.0152(barrels) 240.9265(barrels) 241.8795(barrels) 242.6774(barrels) 243.5842(barrels) 244.5576(barrels) 245.5960(barrels) 246.6067(barrels) 247.6306(barrels) 248.6992(barrels) 249.7561(barrels) 251.0233(barrels) 252.4496(barrels) 253.8411(barrels) 255.1950(barrels) 256.2967(barrels) 257.3668(barrels) 258.4709(barrels) 259.7716(barrels) 260.9407(barrels) 262.0851(barrels) 263.2102(barrels) 264.3499(barrels) 265.4724(barrels) 266.6054(barrels) 267.7189(barrels) 268.4890(barrels) 269.2515(barrels) 270.0463(barrels) 271.1928(barrels) 271.8897(barrels) 272.5868(barrels) 273.5763(barrels) 274.2926(barrels) 275.0795(barrels) 275.9619(barrels) 276.8115(barrels) 277.6830(barrels) 278.5735(barrels) 279.5514(barrels) 280.4642(barrels) 281.4121(barrels) 282.2520(barrels) 283.4003(barrels) 284.2832(barrels) 285.2030(barrels) 286.1273(barrels) 287.2560(barrels) 288.2088(barrels) 289.1347(barrels) 290.0779(barrels) 291.0245(barrels) 291.9758(barrels) 292.9500(barrels) 293.9206(barrels) 294.9176(barrels) 295.9136(barrels) 296.9206(barrels) 297.9417(barrels) 298.9601(barrels) 299.9867(barrels) 301.0085(barrels) 302.0594(barrels) 303.1236(barrels) 304.1550(barrels) 305.8261(barrels) 306.8599(barrels) 307.8688(barrels) 308.8825(barrels) 309.9015(barrels) 311.0789(barrels) 312.0912(barrels) 313.0712(barrels) 314.0447(barrels) 315.0164(barrels) 316.0230(barrels) 317.0047(barrels) 318.0030(barrels) 319.5357(barrels) 320.5816(barrels) 321.7757(barrels) 322.7159(barrels) 323.7273(barrels) 324.7930(barrels) 326.1100(barrels) 327.0773(barrels) 328.0997(barrels) 329.1516(barrels) 330.2475(barrels) 331.3661(barrels) 332.5321(barrels) 333.7481(barrels) 335.0121(barrels) 10.0874(barrels) 10.5355(barrels) 10.9595(barrels) 11.4044(barrels) 11.8919(barrels) 12.3736(barrels) 12.8614(barrels) 13.3980(barrels) 13.8831(barrels) 14.3776(barrels) 14.8988(barrels) 15.3953(barrels) 15.9724(barrels) 16.5014(barrels) 17.0092(barrels) 17.5320(barrels) 18.0658(barrels) 18.6402(barrels) 19.1698(barrels) 19.7197(barrels) 20.2645(barrels) 20.8302(barrels) 21.3894(barrels) 21.9717(barrels) 22.5458(barrels) 23.1349(barrels) 23.7758(barrels) 24.3151(barrels) 24.9446(barrels) 25.5937(barrels) 26.2342(barrels) 26.8109(barrels) 27.4810(barrels) 28.1314(barrels) 28.7518(barrels) 29.4434(barrels) 30.1567(barrels) 30.8012(barrels) 31.4210(barrels) 32.0707(barrels) 32.7920(barrels) 33.4375(barrels) 34.1124(barrels) 34.7723(barrels) 35.5151(barrels) 36.1772(barrels) 36.9242(barrels) 37.6403(barrels) 38.3061(barrels) 39.0379(barrels) 39.7085(barrels) 40.3619(barrels) 41.1410(barrels) 41.8822(barrels) 42.6682(barrels) 43.4188(barrels) 44.2225(barrels) 44.9787(barrels) 45.8253(barrels) 46.5397(barrels) 47.2887(barrels) 48.0107(barrels) 48.7867(barrels) 49.5232(barrels) 50.3517(barrels) 51.2080(barrels) 51.9933(barrels) 52.7723(barrels) 53.5157(barrels) 54.3741(barrels) 55.1975(barrels) 56.0903(barrels) 56.9435(barrels) 57.6158(barrels) 58.3764(barrels) 59.2122(barrels) 60.0122(barrels) 60.7242(barrels) 61.7074(barrels) 62.5137(barrels) 63.2782(barrels) 64.0755(barrels) 64.9365(barrels) 65.7683(barrels) 66.5630(barrels) 67.5343(barrels) 68.4295(barrels) 69.2813(barrels) 70.1081(barrels) 70.9528(barrels) 71.7750(barrels) 72.6352(barrels) 73.5224(barrels) 74.4660(barrels) 75.3671(barrels) 76.3500(barrels) 77.2816(barrels) 78.2814(barrels) 79.1880(barrels) 80.1030(barrels) 80.9920(barrels) 81.8048(barrels) 82.6667(barrels) 83.4551(barrels) 84.4060(barrels) 85.2974(barrels) 86.3482(barrels) 87.2471(barrels) 88.0946(barrels) 89.0605(barrels) 90.0696(barrels) 91.0547(barrels) 92.0191(barrels) 92.9321(barrels) 93.9544(barrels) 94.8820(barrels) 95.8786(barrels) 96.8542(barrels) 97.7960(barrels) 98.7738(barrels) 99.8690(barrels) 0.0979(barrels) 0.1364(barrels) 0.1513(barrels) 0.1711(barrels) 0.1939(barrels) 0.2195(barrels) 0.2483(barrels) 0.2834(barrels) 0.3231(barrels) 0.3685(barrels) 0.4197(barrels) 0.4772(barrels) 0.5415(barrels) 0.6131(barrels) 0.6922(barrels) 0.7793(barrels) 0.8745(barrels) 0.9780(barrels) 1.0898(barrels) 1.2101(barrels) 1.3394(barrels) 1.4775(barrels) 1.6250(barrels) 1.7819(barrels) 1.9483(barrels) 2.1234(barrels) 2.3036(barrels) 2.5079(barrels) 2.7136(barrels) 2.9361(barrels) 3.1605(barrels) 3.3915(barrels) 3.6284(barrels) 3.8737(barrels) 4.1322(barrels) 4.3955(barrels) 4.6715(barrels) 4.9617(barrels) 5.2563(barrels) 5.5645(barrels) 5.8824(barrels) 6.2177(barrels) 6.5691(barrels) 6.9212(barrels) 7.2920(barrels) 7.6738(barrels) 8.0743(barrels) 8.4639(barrels) 8.8751(barrels) 9.2728(barrels) 9.6737(barrels)

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Fracture Length (ft) Fig. 4- Fracture 2 geometry and width distribution after 30 minutes of injection

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Fig. 3- 3D configuration of fractures after stimulating with gelled-LPG

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Reservoir Analysis Using the fracture network obtained in Fig.3, coupling through numerical simulator RESOLVE was established. Table 1 details the values of the parameters used in the simulations, and Fig.7 shows the reservoir boundaries and the fracture network. It should be kept in mind that the matrix permability in the SRV will be higher than that in XRV (External Reservoir Volume). The permeability within the SRV is likely to be enhanced due to the induced fractures and the simultaneous activation of the natural fracture network.

SPE 167

Table 1- Parameter values used in reservoir simulation/coupling

Parameter Drainage area Layer properties Reservoir Pressure(psia) Matrix permeability(x, y and z direction)(nD) Layer Thickness(ft) Net to Gross ratio(unitless) Residual Water Saturation (%) Langmuir Pressure(psia) Langmuir Volume(scf/ton) Bulk Density(g/cc) Well/Completion Wellbore Radius(ft) Average Fracture Half Length(ft) Average Fracture Width(in) Fracture Conductivity(md-ft) Fluid Properties Bottomhole Temperature(°F) Seperator Gas Gravity Conditions Producing Flow rate(Mscf/day)

Value 120 acres 2500 500 100 0.5 0.25 500 70 2.54 0.3 355 0.26 Infinite Conductivity 100 0.65 100

The different flow regimes in a fractured shale medium have been documented in various literatures in the past. However, to refresh, they are explained briefly: 1. Internal linear transient flow– The most dominant flow regime in the history of a shale well as flow orginates from the enhanced matrix in the SRV and flows into the fracture. This regime might last from several days to years based on factors such as matrix permeability, fracture permeability and drawdown. 2. Internal depletion flow - This flow period begins at the start of interference between fractures, and is also characterized as boundary dominated flow. 3. External linear transient flow - This flow period happens when the SRV is depleted but the depletion front has still not reached the drainage area available to the well. There might be flow regimes preceding this linear flow regime (such a radial/elliptical flow). However, these regimes might not be dominant as the linear flow regime. 4.

Drainage volume depletion flow - This flow period is characterized by a pseudo-steady state flow from the drainage volume once a well’s performance has been affected by its drainage boundaries.

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SPE 167105

Fig. 7- Reservoir boundaries and fracture network replicated in RESOLVE

Alongside monitoring the flowing bottomhole pressure (FBHP) and the Expected Ultimate Recovery (EUR), the movement of the pressure front was studied at various timesteps. Since only a single stage case was modeled, time period to observe fracture stage interference was not possible. The pressure contours at various time periods are shown in Fig.8, Fig. 9 and Fig. 10. Additionally, the EUR and BHP are shown in Fig. 11 and Fig. 12. a

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Fig. 8- Pressure contours at (a) 1 day and (b) 25 days

SPE 167105

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SPE 167105

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SPE 167105

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Pressure/Stress Dependent Permeability (SDP) Pressure/Stress dependent permeability is believed to occur in deep over-pressured formations such as the Haynesville Shale. As the reservoir pressure depletes due to production, the net overburden stress increases 4 resulting in a loss of matrix permeability. SDP can be described by the functional form shown in Fig.13 [Friedel] , where σ refers to the overburden stress, the subscript i refers to initial conditions, and α is the permeability loss 5 exponent .

Fig. 13- Compaction reduction in permeability formations

Since the shale play considered in this case is shallow and normally pressured, SDP does not have a major effect. However, we can observe from Fig.14 that, there might be a slight change in the FBHP towards the late part of the production period, but it is not significant. 3000

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SPE 167105

Conclusions With this work, we researched an alternative form of fracturing in shales, and the following observations were made 1. Fracturing using a gaseous medium by using high energy pulses might be a viable alternative to hydraulic fracturing. 2. Under favorable reservoir and geomechanical conditions, pulsed fracturing (PF) can create multiple fractures that radiate away from the wellbore. 3. This network can further be extended into the reservoir by pumping gas at a reduced rate and for an extended amount of time (i.e. pulsed extended gas fracturing: PEGF). 4. Coupling of the generated fracture network pattern with a reservoir simulator will help in quantifying the production efficiency of these fractures, and can serve as a source to compare with the efficiency of hydraulic fractures. 5. The effect of stress dependent permeability is usually more pronounced in deep and overpressured shales. 6. The current work focuses on a single stage fracturing scenario. But this will be extended into a multi stage scenario in the future. References 1. T. Blanton, "Material properties of devonian shale for stimulation - Technology development", United States, DOE, 1980. 2. M.R. Safari, R. Gandikota, U. Mutlu, M. Ji, J. Glanville, H. Abass, "Pulsed Fracturing in Shale Reservoirs: Geomechanical Aspects, Ductile-Brittle Transition and Field Implications", SPE/AAPG Unconventional Resource Technology Conference, SPE 1579760, Denver, Colorado, USA, 2013. 3. L.H. Ribeiro, M.M. Sharma, "A New Three-Dimensional Compositional Model for Hydraulic Fracturing with Energized Fluids", SPE Annual Technical Conference and Exhibition, SPE 159812, San Antonio, Texas, USA, 2012. 4. Friedel, T., “Numerical simulation of production from tight-gas reservoirs by advanced stimulation technologies”, Universit\ätsbibliothek der TU BAF, 2005. 5. A. Boulis, R. Jayakumar, C. Nyaaba, R. Rai, V. Sahai, “Challenges Evaluating Shale Gas Well Performance: How Do We Account For What We Don’t Know?”, IPTC 16396, Being, China, 2013