Summary Acid jetting occurs as a result of pumping acid through limited-entry liner completions, causing high-velocity streams to impinge against the wellbore wall. The dissolution effect of jetting differs significantly from conventional matrix acidizing. Acid jetting causes cavities to be formed at the points of contact of the jet with the rock, with wormholes forming beyond the cavity. Jetting has been shown to be an effective technique for placing acid along extended-reach laterals, removing filter cake, and enhancing wormhole propagation. The velocity of the impinging jet and its standoff distance from the rock cause some of the acid to penetrate the formation and some to flow back in the annular space of the liner. Two types of dissolution mechanisms occur: surface dissolution forming the cavity and matrix dissolution forming the wormholes. These dissolution mechanisms are highly dependent on the acid-injection rate, velocity of the jet, temperature, and permeability of the formation. The differences between the matrix dissolution mechanism of acid jetting and that of conventional matrix acidizing are most obvious at low acid-injection rates. Experiments were performed with the intention of quantifying the difference in pore volume (PV) to breakthrough between acid jetting and matrix acidizing, as well as determining the effect of increased temperature, rock permeability, and acid concentration on this value with respect to the acid-injection rate. The baseline parameters of room temperature, 15% hydrochloric (HCl) acid, and 2- to 4-md Indiana limestone were individually compared with experiments run at 180°F, 28% HCl, and Indiana limestone cores of 30, 60, and 140 md. The effect of jetting velocity was also investigated. A direct comparison with conventional matrix acidizing was made by eliminating the jetting effect of the stream through mechanical dispersion. Acid jetting creates a point of heightened interstitial velocity at the contact of the acid and the rock, causing wormhole propagation to occur at a faster rate than it would in conventional matrix acidizing at that injection rate. This effect is especially pronounced as the jetting velocity is increased above that of matrix acidizing, and it tapers off at progressively higher jetting velocities.

We describe the successful application of a new method to estimate permeability and permeability anisotropy from transient measurements of pressure acquired with a wireline straddle-packer formation tester. Unlike standard algorithms used for the interpretation of formation-tester measurements, the method developed in this paper incorporates the physics of two-phase immiscible flow as well as the processes of mudcake buildup and invasion.An efficient 2D (cylindrical coordinates) implicit-pressure explicit-saturation finite-difference algorithm is used to simulate both the process of invasion and the pressure measurements acquired with the straddle-packer formation tester. Initial conditions for the simulation of formation-tester measurements are determined by the spatial distributions of pressure and fluid saturation resulting from mud-filtrate invasion. Inversion is performed with a Levenberg-Marquardt nonlinear minimization algorithm. Sensitivity analyses are conducted to assess nonuniqueness and the impact of explicit assumptions made about fluid viscosity, capillary pressure, relative permeability, mudcake growth, and time of invasion on the estimated values of permeability and permeability anisotropy.Applications of the inversion method to noisy synthetic measurements include homogeneous, anisotropic, single-and multilayer formations for cases of low-and high-permeability rocks. We also study the effect of unaccounted impermeable bed boundaries on inverted formation properties. For cases where a priori information can be sufficiently constrained, our inversion methodology provides reliable and accurate estimates of permeability and permeability anisotropy. In addition, we show that estimation errors of permeability inversion procedures that neglect the physics of two-phase immiscible fluid flow and mud-filtrate invasion can be as high as 100%. MethodThere are three main components in the workflow developed in this paper:1. Mud-filtrate invasion algorithm 2. Two-phase axisymmetric simulator 3. Nonlinear minimization algorithm Transient measurements of pressure and flow rate are compared to the outputs of a two-phase axisymmetric simulator to yield new model parameters through nonlinear minimization. The invasion algorithm makes use of these parameters (permeability and permeability anisotropy), in addition to pressure overbalance, invasion geometry, mudcake properties, and other rock-formation properties, to simulate the process of mud-filtrate invasion. Subsequently, the calculated spatial distributions of pressure and fluid saturation resulting from mud-filtrate invasion are used as initial conditions for pressure-transient tests. To reduce the time required by the inversion, this last step could be approximated with an invariant mud-filtrate invasion profile calculated only once during the minimization. However, such a strategy is not recommended for supercharged formations where updates of initial conditions during minimization can drastically impact inversion results. For the synthetic case examples cons...

Just-In-Time-Perforating (JITP) was developed by ExxonMobil over a decade ago to improve multi-zone stimulation in vertical and S-shaped wells in the Piceance basin, Colorado. With this technology, multiple single-zone fracture stimulations are performed on a single wireline run using ball sealers and perforating guns that remain downhole during the fracturing treatment. This results in substantial cost reduction and productivity uplift because perforation intervals are individually and effectively treated one at a time with less horse power, smaller number of frac plugs, and fewer wireline runs. The method has been successfully implemented by ExxonMobil in more than 350 wells and over 10,000 treatments and is licensed to a number of service companies.There is substantial business incentive to implement the JITP technique in horizontal wells, extensively used in unconventional gas developments. With XTO Energy joining ExxonMobil, the global gas portfolio incremented by 45 trillion cubic feet. This includes conventional gas, shale gas as well as other unconventional resources, such as tight gas, coal bed methane, and shale oil. This paper presents the first application of JITP in horizontal wells. Operations were conducted in the Fayetteville Shale, Arkansas. The paper discusses advantages and disadvantages of the method as well as lessons learned from pre-field trials and full-well implementations. Critical to the success of the initial technology application was the enforcement of a structured approach which included technical feasibility studies, contractor qualification, pre-field trials, well candidate selection, and a deployment plan to capture learnings and best practices. Pre-field trials were executed in several wells to test potential technical/operational concerns, such as sand build-up around perforating guns, fluid diversion with buoyant and non-buoyant ball sealers, and the ability to move guns through the lateral. Preliminary field costs and production performance in horizontal wells are promising and support continued deployment of the technology.

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Autonomous downhole tools offer a range of advantages over conventional tools controlled manually via umbilicals. For instance, perforating guns or bridge plugs could be dropped or pumped downhole without the use of wireline (slick or electric line), coiled tubing or tractors. Because umbilical intervention is no longer required, the tools may automatically perform an action (e.g., perforate a desired interval) with substantial cost reduction and enhanced safety. The elimination of wireline lubricators, lifting equipment, wires, additional personnel and vehicles minimizes the potential for accidents in this already confined space. This is particularly important during hydraulic fracturing operations where this method may enable faster pumping rates and increased fracture volumes during daylight hours. Use of this technology will also reduce air emissions from support equipment that would no longer be required. This paper describes an autonomous perforating tool currently being developed by ExxonMobil Upstream Research Company. This patent pending technology is based on using a self-destructing disposable perforating tool which is run without a wireline. To accomplish this objective, the custom designed tool has three frangible components: 1) a logging device; 2) an on-board navigation system; and 3) friable perforating guns. The on-board navigation system reads the log signals and performs real-time processing of the depth data. Upon matching of the desired depth, the system issues a firing command to the friable perforating gun assembly. The latter simultaneously initiates the self-destruction of the tool. Thus, the tool is completely destroyed after perforating and the remaining debris fall to the bottom of the hole, where they could be left, flowed back to surface or removed during cleanup prior to tubing installation. The volume of debris is small and does not require drilling additional rat hole. The delivery of the tool is achieved by either gravity free-falling in low-angle wells or by pumping it downhole during hydraulic fracturing or any other pumping operation in high-angle or horizontal wells. An important part of the overall design is the safety system built into the tool to make the system as safe as, or safer than currently used perforating practices.