Recently, it has been shown that for a dynamical black hole in any higher derivative theory of gravity, one could construct a spatial entropy current, characterizing the in/outflow of entropy at every point on the horizon, as long as the dynamics of the amplitude is small enough. However, the construction is very much dependent on how we choose the spatial slicing of the horizon along its null generators. In this note, we have shown that though both the entropy density and the spatial entropy current change nontrivially under a reparametrization of the null generator, the net entropy production, which is given by the 'time' derivative of entropy density plus the divergence of the spatial current is invariant. We have explicitly verified this claim for the particular case of dynamical black holes Einstein-Gauss-Bonnet theory.1 We are deeply saddened to lose our friend and collaborator, Pooja Jethwani. She was an active collaborator in this project and had seen its completion before the end of our time together.
Acid systems are widely recognized by the oil and gas industry as an attractive class of fluids for the efficient stimulation of carbonate reservoirs. One of the major challenges in carbonate acidizing treatments is adjusting the convective transport of acid deep into the reservoir while achieving a minimum rock face dissolution. Conventional emulsified acids are hindered by several limitations; low stability at high temperatures, a high viscosity that limits pumping rate due to frictional losses, the potential of formation damage, and the difficulty to achieve homogenous field-scale mixing. This paper highlights the successful application of an engineered low-viscosity retarded acid system without the need for gelation by a polymer or surfactant or emulsification by diesel. An acid stimulation job using a new innovative retarded acid system has been performed in a West Kuwait field well. The proposed acid system combines the use of a strong mineral acid (i.e. hydrochloric acid "HCl") with a non-damaging retarding agent that allows deeper penetration of the live HCl acid into the formation, resulting in a more effective stimulation treatment. The retardation behavior testing includes dissolution experiments, compatibility testing, coreflood study, and corrosion rate testing (conducted at 200°F). The on-job implementation included the use of a packer to pinpoint fluid pumping (pre-flush) at the point of interest, followed by the customized novel retarded acid system for improving conductivity at perforations and effective reservoir stimulation. This acid system is characterized by having a low-viscosity and high thermal stability system that can be mixed on the fly. This approach addresses the main challenges of emulsified acid systems and offers a cost-effective solution to cover a wide range of applications in matrix acid stimulation and high-temperature conditions that require a chemically retarded acid system. The application of this novel acid retarded system is a fit-for-purpose solution to optimize the return on investment by maximizing the well production and extending the lifetime of the treatment effect. This new system also offers excellent scale inhibition and iron control properties which eliminates the need for any acid remedial work, making it an economical approach over other conventional acid systems. The paper presents results obtained after stimulating the carbonate reservoir and describes the lessons learned from the job planning and execution phases, which can be considered as a best practice for application in similar challenges in other fields. Proper candidate selection, best available placement technique, and lab-tested formulation of novel retarded acid system resulted in achieving 1700 BOPD of oil production (27% higher than expected).
Derivative expansion and large-D expansion are two perturbation techniques, which are used to generate dynamical black-brane solutions to Einstein's equations in presence of negative cosmological constant. In this note we have compared these two techniques and established the equivalence of the gravity solutions generated by these two different techniques in appropriate regime of parameter space up to first non-trivial order in both the perturbation parameters for Einstein-Maxwell systems, generalizing the earlier works of [1,2] for non-charged systems. An one-toone map between dynamical black-brane geometry and AdS space, which also exists at finite number of dimensions, has also been established. Contents 1 Introduction : 1.1 Strategy 2 Review of Hydrodynamics from charged black-branes in arbitrary dimensions : 2.1 Scalars at first order 2.2 Vectors at first order 2.3 Tensors at first order 2.4 The global metric and gauge field at first order 2.5 The boundary stress tensor and the charge current 2.6 Hydrodynamic metric and gauge field up to first order in derivative 3 The large D metric, gauge field and membrane equations: 3.1 The dual system 4 Comparing fluid-gravity and membrane-gravity dualities : 4.1 The split of the hydrodynamic metric 4.2 Membrane data in terms of fluid data 4.2.1 Determining ψ 4.2.2 Determining U A 4.2.3 Determining Q 4.2.4 Relevant derivatives of the basic data 4.3 Comparing the metrics and gauge fields 4.3.1 Comparing the gauge fields 4.3.2 Comparing the metric 4.4 Comparing the evolution of two sets of data 5 Conclusons and future directions : A The Large-D limit of the integrations appearing in hydrodynamic metric A.1 Analysis of the integral in the function F 1 A.2 Analysis of the integral in the function F 2 B The inverse of the background metric and christoffel symbols w.r.t background metric C Notation 34
Increasing water cut in oil-producing zones is a common issue, particularly in mature fields. Currently, most decisions are governed by economics, and incurring additional expenses, such as handling produced water, is undesirable. Depending upon the source of the water production, chemical isolation provides one effective solution to this issue. This paper describes a cost-effective coiled tubing (CT) intervention to implement permanent zonal isolation for water shutoff using an organically crosslinked polymer (OCP) sealant system and a modified organically crosslinked polymer (m-OCP) sealant system to provide a controlled, shallow penetration solution to the problem in a high-permeability, low-pressure reservoir. The traditional water shutoff method uses rig intervention for cement squeezes, which targeting shallow penetration can be time consuming and expensive in a high-permeability, low-pressure reservoir. The OCP sealant system is an organically crosslinked polymer that is thermally activated to effectively seal the targeted interval. The m-OCP sealant system combines particulates with the OCP sealant system to provide leakoff control to help promote shallow matrix penetration. The production logging tool (PLT) data for the candidate well indicated that the maximum water cut originated from the lower perforations and a single zone. CT intervention was selected to accurately place the OCP and m-OCP sealant systems and to permanently block water production by creating polymer barriers inside the reservoir and to remove any remaining OCP/m-OCP from the wellbore. OCP and m-OCP are resistant to acid and H2S and provide the required radial penetration. This system provides a predictable and controlled set time (as shown by laboratory testing). Because this system does not develop compressive strength, a simplified cleanout with a jetting nozzle is required to wash it from the well. After completing the zonal isolation with the OCP sealant system, the pressure test for the zone indicated a good seal. An electric submersible pump (ESP) was run on the completion string, and initial test results showed that the water cut was reduced from 97 to 75%, and oil production increased from 175 to 300 bpd. Increased production will recover all intervention and chemical costs within 20 days. The polymer sealant system with the customized intervention solution successfully reduced the water cut for this west Kuwait field. The same approach can be applied to other similar fields worldwide.
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