A three dimensional geomechanical model was built using commercially available Finite Element Analysis (FEA) software to simulate propagating hydraulic fracture (HF) and its interaction with a vertical natural fracture (NF) in tight medium. The approach initially involved studying simple three dimensional single layered model followed by complex three layered model. The main area of concern was the fluid continuity at the HF-NF intersection. Different approaches were considered to model this fluid continuity. Finally, newly introduced elements were used for modeling the intersection of the NF-HF planes. These elements have ability to model the fluid continuity at HF-NF intersection. It was observed that for high stress contrast the NF activated length is smaller compared with the low stress contrast. For high stress contrast with principal horizontal stresses reversed, the HF intersects, activates and opens the NF. Increasing the injection rate results in longer and wider HF but does not significantly affect the NF activated length. Injection fluid viscosity shows an inverse relationship with HF length and a proportional relationship with HF opening or width as well as with NF length. It was observed that a weak NF plane temporarily restricts the HF propagation. On the other hand, a tougher NF or a NF with properties similar to surroundings does not show this type of restriction. The NF activated length was found maximum in the case of weaker NF and nearly zero in the case of stronger NF and NF similar to surroundings. This paper presents the results for a three layered, three dimensional geomechanical model with single HF and NF orthogonally intersecting each other, using the newly introduced cohesive elements for the first time in technical literature. Further a detailed sensitivity analysis considering the effect of stress contrast, injection rate, injection fluid viscosity and NF properties on this HF-NF interaction was conducted.

Field X in Rajasthan, India has been developed with 22 Injectors wells & 40 Producers wells. Most of the producers are completed with standalone screens of different types like conventional, ICD's and SSD types. Almost 60% of the producers are completed with ICD type screens. The open hole for screens section has been drilled with 10.2 ppg SBDIF (Synthetic based drilling fluid) which includes dolomite and barite as weighting agents. After running the screens, the screen section is displaced with 8.4 ppg low weight SBDIF (Synthetic based Drill-In Fluid) which has organophilic clay (Viscosifier) and emulsifier as the key components. Due to some operational delay in bringing the wells online, mud was left inside the screens for a few months. The deposition of mud filter cake and heavier hydrocarbon probably choked the ICD screens ensuing a number of ICD's non-contributing. Conventional stimulation techniques didn't help in achieving good results.To effectively remove the suspected damage a coiled tubing based solution was implemented which involved the application of Inflatable Straddle Packer tool. It provides pinpoint accuracy for conventional, horizontal and multilateral stimulation treatments. Coiled Tubing Conveyed Re-Settable selective straddle packer elements allow multiple settings in one trip. Treatment Valve allows precise injection of treatment fluid & adjustable element spacing helps in straddling the long interval.A case history of successful application of CT conveyed inflatable straddle apcker tool in field X in India is presented in this paper which enabled the correct placement of a series of stimulating chemicals targeting different damage mechanisms i.e. wax deposition, mud filter cake, inorganic scaling etc. Post stimulation production logs showed excellent improvement of conformance in zonal contributions.The learning from this stimulation technique was also applied to the horizontal wells in field Y with very encouraging results. Introduction:Field X & field Y lie within a narrow rift basin formed during the Palaeocene epoch. The Oil is contained in the Z group sandstones consisting of approximately 250 m of medium to thick bedded fine to coarse grained sandstones interbedded with mudstones. The sands were deposited in a variety of braided to sinuous meandering channels and are composed almost entirely of mature quartz grains. The Z group has been subdivided into five units on a lithostratigraphic basis. At X field, they are designated ZX1 to ZX5 & at Y field, they are designated as ZY1 to ZY5. The lower part of the Z formation is dominated by well-connected sheet flood and braided channel sands, whilst the Upper Z formation is dominated by more sinuous, laterally migrating fluvial channel sands.The fields contain excellent reservoir quality sands with porosities of 18 to 33 % (average 25%) and permeabilities of upto 20 darcies (average 5 darcies). The fields contain waxy sweet crude oil with API gravity ranging from 20ºAPI near the OWC to 30ºAPI higher in the oil column (average ~27ºAPI). The ...

Summary We built a 3D geomechanical model using commercially available finite–element–analysis (FEA) software to simulate a propagating hydraulic fracture (HF) and its interaction with a vertical natural fracture (NF) in a tight medium. These newly introduced elements have the ability to model the fluid continuity at an HF/NF intersection, the main area of concern. We observed that, for a high–stress–contrast scenario, the NF cohesive elements showed less damage when compared with the low–stress–contrast case. Also, for the scenario of high stress contrast with principal horizontal stresses reversed, the HF intersected, activated, and opened the NF. Increasing the injection rate resulted in a longer and wider HF but did not significantly affect the NF–activated length. Injection–fluid viscosity displayed an inverse relationship with the HF length and a proportional relationship with the HF opening or width. We observed that a weak NF plane temporarily restricts the HF propagation. On the other hand, a tougher NF, or an NF with properties similar to its surroundings, does not show this type of restriction. The NF activated length was found at its maximum in the case of a weaker NF and at nearly zero in the case of a stronger NF and an NF that has strength similar to its surroundings. In this study we present the results for a three–layered 3D geomechanical model with a single HF and NF orthogonally intersecting each other, using newly introduced cohesive elements for the first time in technical literature. We also conducted a detailed sensitivity analysis considering the effect of stress contrast, injection rate, injection–fluid viscosity, and NF properties on this HF/NF interaction. These results provide an idea of how the idealized resultant fracture geometry will change when several fracture/fracture treatment properties are varied.

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