It is a great challenge to divert acid into untreated zones in a thick, heterogeneous, and high permeability sandstone formation. The heterogeneity can be created by hydraulic fracturing, acidizing, or the nature of the reservoir. Common diverting agents do not work well in these situations. In high permeability porous media, foam has the tendency to segregate, gaseous phase will occupy smaller pores while the aqueous phase occupies the larger pores1. Due to the relative permeability effect, the higher permeability streaks becomes the preferable path for acid treatment fluids2. Therefore, limited effective diversion can be achieved by foam. Other diverting agents rely on particulate matter or polymer solution to plug off thief zones temporarily. However, the invasion of the undissolved particles and polymer residue can cause further formation damage. Owing to its rheological properties, and its lack of solids, Visco-Elastic-Surfactant diverting agents (VESDA) have been proven to be effective for acid diversion in carbonate formations3, where large flow channels are generated due to acid-rock reaction. This current study extends the application into diversion in high permeability, highly heterogeneous sandstone formations. Throughout this paper, the term VESDA is used to refer to the VES diverting agent. Laboratory tests have shown that VES is capable of increasing the flow resistance in the high permeability rock (simulated by a proppant pack) and will divert treatment fluid into the low permeability sandstone matrix. The process was more efficient if multiple stages of alternating VES and acid were used. Field case histories in Gulf of Mexico are also presented in this study to demonstrate the effectiveness of the VES material for acid diversion in the highly permeable and heterogeneous sandstone reservoirs. Introduction When a well penetrates through multiple zones in a heterogeneous reservoir, it is difficult to treat all of the zones evenly during matrix acidizing. Job design and fluid selection need to be made by considering the permeability contrast, saturation4 in the formation, and availability of the material. On deep water offshore platforms, the problem is further complicated by the space constraint and transportation of the chemicals. Commonly used diverting agents include polymer gels, foams, oil soluble solids materials5, and rock salt. These materials either require more complex process, such as foam, or fail to reach the full stimulation potential due to damage induced by residue precipitation, saturation alteration, or solid invasion. VESDA overcomes these difficulties by providing a easy, effective, and clean solution to the acid diversion process. Reservoirs in the deep water of the Gulf of Mexico are normally completed by gravel pack or frac-n-pack, due to their sand producing tendency. Frequently, a fluid loss control pill is required during well completion operations after perforating. Therefore, before gravel pack or frac-n-pack, a matrix acidizing job will be performed to cleanup up the remaining drilling, perforating, and pill damage. Because of the high permeability of these formations, acid diversion is a challenging task. Foam segregation can cause the acid to preferentially enter the higher permeability layers, leaving the formation partially treated. Solid-containing diverting agents can invade into the matrix causing additional damage. This defeats the purpose of acidizing treatment. The VESDA possesses the unique characteristic of being more viscous in the aqueous phase and non-viscous in the hydrocarbon phase. When it enters the acid treated zone, which is fully saturated by an aqueous phase (acid) near the wellbore, its viscosity becomes a resistance to the following treating fluid. Thus the treating fluid has to enter the zones that are still highly saturated by hydrocarbon. The VESDA also cleans up easily without leaving any residue upon contacting liquid hydrocarbon during flow back. Hence the full benefit of the acid stimulation can be achieved.

This paper continues the investigation of interwell fracturing interference for an infill drilling scenario synthetic case based on Eagle Ford available public data and explores pressure and stress-sink mitigation strategies applied to the simulation cases developed in the previous publication (SPE 174902). Emphasis is given to refracturing scenarios, given the intrinsic restimulation value for depleted parent wells and the strategic importance due to the current low oil prices. The stress and pressure depletion methodology is expanded in this paper, adding a refracturing scenario before the infill child well is stimulated. Changes in stress magnitudes and azimuths caused by new and reactivated fractures are calculated using a finite element model (FEM). After refracturing the parent well, modeling shows that stress deflection and repressurization of the originally depleted production zone will reduce subsequent fracture hits from infill wells. The first mechanism to reduce fracture hits is the stress realignment, which promotes transverse fracture propagation from the infill well away from the parent well. The second fracture-hit-reduction mechanism is repressurization of depleted zones to hinder fracture propagation in lower-pressure zones. Prevention of fracture hits by active deflection results in an increased stimulated reservoir volume (SRV) for both the parent and child wells. Overall pad level and individual wellbore cumulative production experience a significant increase due to increased SRV. With proper reservoir and geomechanical data, this approach can be applied in a predictive manner to decrease fracture-hit risk and improve overall recovery. This workflow represents the first comprehensive multidisciplinary approach to coupling geomechanical, complex hydraulic fracture models, and multiwell production simulation models aimed towards understanding fracture-hit reduction using refracturing. The workflow presented can be applied to study and design an optimum refracturing job to prevent potentially catastrophic fracture hits during refracturing operations.

Schlumberger and four Eagle Ford Shale Play operators drilling in South Texas joined a consortium initiative to acquire various types of open hole logging data in several horizontal wells, and use the data to design the completions with optimum fracture stage and perforation cluster positioning. Horizontal production logs were subsequently used to gauge the effectiveness of using the log data to engineer the completions. This paper outlines the data acquisition techniques, analyses made on that data, application, results and conclusion.

It is a great challenge to divert acid into untreated zones in a thick, heterogeneous, and high permeability sandstone formation. The heterogeneity can be created by hydraulic fracturing, acidizing, or the nature of the reservoir. Common diverting agents do not work well in these situations. In high permeability porous media, foam has the tendency to segregate, gaseous phase will occupy smaller pores while the aqueous phase occupies the larger pores1. Due to the relative permeability effect, the higher permeability streaks becomes the preferable path for acid treatment fluids2. Therefore, limited effective diversion can be achieved by foam. Other diverting agents rely on particulate matter or polymer solution to plug off thief zones temporarily. However, the invasion of the undissolved particles and polymer residue can cause further formation damage. Owing to its rheological properties, and its lack of solids, Visco-Elastic-Surfactant diverting agents (VESDA) have been proven to be effective for acid diversion in carbonate formations3, where large flow channels are generated due to acid-rock reaction. This current study extends the application into diversion in high permeability, highly heterogeneous sandstone formations. Throughout this paper, the term VESDA is used to refer to the VES diverting agent. Laboratory tests have shown that VES is capable of increasing the flow resistance in the high permeability rock (simulated by a proppant pack) and will divert treatment fluid into the low permeability sandstone matrix. The process was more efficient if multiple stages of alternating VES and acid were used. Field case histories in Gulf of Mexico are also presented in this study to demonstrate the effectiveness of the VES material for acid diversion in the highly permeable and heterogeneous sandstone reservoirs. Introduction When a well penetrates through multiple zones in a heterogeneous reservoir, it is difficult to treat all of the zones evenly during matrix acidizing. Job design and fluid selection need to be made by considering the permeability contrast, saturation4 in the formation, and availability of the material. On deep water offshore platforms, the problem is further complicated by the space constraint and transportation of the chemicals. Commonly used diverting agents include polymer gels, foams, oil soluble solids materials5, and rock salt. These materials either require more complex process, such as foam, or fail to reach the full stimulation potential due to damage induced by residue precipitation, saturation alteration, or solid invasion. VESDA overcomes these difficulties by providing a easy, effective, and clean solution to the acid diversion process.

Although numerous sandstone and carbonate simulators have been developed during the past decade, few have been field validated. This paper addresses the field validation of a numerical simulator used for treatment design. Five matrix acidized wells were used for validation of the simulator. In most cases the simulator was within +10% of the actual skin reduction observed in the well. The simulator calculates the pressure at the formation face and within the multiple layers along the corresponding flow rates. Diversion and mineral dissolution with the corresponding permeability changes are also calculated for sandstone and carbonates. The key to simulator validation is good well data including pre and post-treatment pressure buildup analysis, PLT data, log and/or core data, formation mineralogy and the knowledge of the damage mechanism. Simulations indicate previously developed "rule of thumb" guidelines for mud acid volume may not yield the best results. When formation damage is shallow, as in some of the case histories the "rule of thumb" may results in the use of excessive acid, whereas, when damage is 2 to 3 feet from the wellbore higher volumes of acid are normally required. Simulations support the concept that diversion is essential and can easily be observed via the flow per layer output. This study indicates matrix treatment design is not engineered until it is simulated using valid models. Application of the validated simulator results in increased production and improved economics for the operator. A detailed description of the validation process and the supporting well data are presented. Introduction Sandstone matrix acidizing using mud acid formulations has been used for decades to remove siliceous formation damage. The damage can be formed during drilling, completion and/or production phases of a well, which can cause severe production decreases. Numerous papers have been written on laboratory and field studies directed at clay damage removal. These laboratory studies were conducted in support of development of acidizing simulators. However, none of the simulators were field validated. This paper will address this issue by using well documented case histories. The numerical simulator used in this study was previously described in the literature. The simulator is 2d and is capable of acidizing and diverting fluids. Fluid fingering, acid concentrations and fluid saturation at each point radially in the formation are calculated at each time step. The model considers diversion by using cake resistance or a pseudoskin correlation. Dissolution of the mineral species is based on a change in porosity. The porosity is converted to permeability based on a modified Labrid's formula. The three sandstone cases presented are graveled pack wells from the Gulf of Mexico. Two wells were suspected to have HEC polymer damage and the third well was suspected to have silt and clay damage. Information for each of the wells varied from detailed laboratory flow studies to porosity logs. The later is probably what most operators have for their well description. In all three cases we were able to model the pre and post skin results. The two carbonate cases are wells from the Middle East. They represent the acids used routinely in carbonate reservoirs (HCl and emulsified HCl). Two distinct models are used in the simulator process. The first model is cable of modeling wormhole growth used for non-retarded HCl whereas the second model assumes uniform dissolution by a emulsified (retarded) acid i.e. radial flow through all pore throats. Sandstone Acidizing Validation Case Histories Modeling. During sandstone acidizing the numerical simulator models the dissolution of formation damage and native minerals. P. 283^