Correction of source-rock permeability measurements owing to slip flow and Knudsen diffusion: a method and its evaluation

Source-rock permeability is a key parameter that controls the gas production rate from unconventional reservoirs. Measured source-rock permeability in the laboratory, however, is not an intrinsic property of a rock sample, but depends on pore pressure and temperature as a result of the relative importance of slip flow and diffusion in gas flow in lowpermeability media. To estimate the intrinsic permeability which is required to determine effective permeability values for the reservoir conditions, this study presents a simple approach to correct the laboratory permeability measurements based on the theory of gas flow in a micro/nano-tube that includes effects of viscous flow, slip flow and Knudsen diffusion under different pore pressure and temperature conditions. The approach has been verified using published shale laboratory data.The ＇＇corrected＇＇（or intrinsic） permeability is considerably smaller than the measured permeability. A larger measured permeability generally corresponds to a smaller relative difference between measured and corrected permeability values. A plot based on our approach is presented to describe the relationships between measured and corrected permeability for typical Gas Research Institute permeability test conditions. The developed approach also allows estimating the effective permeability in reservoir conditions from a laboratory permeability measurement.

Local events-based fast RTM surface-offset gathers via dip-guided interpolation

Reverse Time Migration(RTM)Surface Ofset Gathers(SOGs)are demonstrated to deliver more superior residual dip information than ray-based approaches.It appears more powerful in complex geological settings,such as salt areas.Still,the computational cost of constructing RTM SOGs is a big challenge in applying it to 3D feld data.To tackle this challenge,we propose a novel method using dips of local events as a guide for RTM gather interpolation.The residual-dip information of the SOGs is created by connecting local events from depth-domain to time-domain via ray tracing.The proposed method is validated by a synthetic experiment and a feld example.It mitigates the computational cost by an order of magnitude while producing comparable results as fully computed RTM SOGs.

自适应走时校正的Marchenko地震成像

Marchenko地震成像通过求解Marchenko方程重构完整的单程格林函数来对地下反射界面成像,能压制常规成像方法中的层间多次波偏移假像,且该成像方法可以仅对指定的目标区域成像。速度模型的正确与否会影响成像点到地面的直达波估计,从而导致求解Marchenko方程得到的单程格林函数不精确,影响最终的Marchenko成像结果。针对该问题,本文基于等旅行时原则提出了自适应走时校正的Marchenko成像方法。该成像方法基于等时原则计算速度模型不准确引起的直达波旅行时时差偏移量,并根据该偏移量直接校正不正确的直达波,重构正确的格林函数,从而使得成像结果在一定程度上不受错误速度模型的影响,提高了在速度模型不准确情况下的Marchenko成像质量。通过合成数据测试实验,对比分析了常规Marchenko成像和改进的Marchenko成像的结果,验证了在速度模型不正确的情况下,自适应走时校正的Marchenko成像方法能在一定程度上将地震波场归位,得到相对正确的地质结构。

A comprehensive review on proppant technologies

The main function of traditional proppants is to provide and maintain conductive fractures during well production where proppants should meet closure stress requirement and show resistance to diagenesis under downhole conditions.Many different proppants have been developed in the oil&gas industry,with various types,sizes,shapes,and applications.While most proppants are simply made of silica or ceramics,advanced proppants like ultra-lightweight proppant is also desirable since it reduces proppant settling and requires low viscosity fluids to transport.Additionally,multifunctional proppants may be used as a crude way to detect hydraulic fracture geometry or as matrices to slowly release downhole chemical additives,besides their basic function of maintaining conductive hydraulic fractures.Different from the conventional approach where proppant is pumped downhole in frac fluids,a revolutionary way to generate in-situ spherical proppants has been reported recently.This paper presents a comprehensive review of over 100 papers published in the past several decades on the subject.The objectives of this review study are to provide an overview of current proppant technologies,including different types,compositions,and shapes of proppants,new technologies to pump and organize proppants downhole such as channel fracturing,and also in-situ proppant generation.Finally,the paper sheds light on the current challenges and emphasizes needs for new proppant development for unconventional resources.

Methane oxidation by green oxidant to methanol over zeolite-based catalysts

To reduce greenhouse gas emission from oil and gas production,it is essential to better convert methane to useful chemicals(rather) than to flare it.Conversion of methane to liquid oxygenates(mainly methanol) has attracted extensive attention and countless efforts have been made;however,running this reaction in a green,efficient,and practical way has remained elusive.The novel catalyst and oxidants play a critical role in activating methane and converting it to oxygenates(methanol).In this review,the work of commonly used oxidants for methane partial oxidation have been summarized,in which,earth abundant oxidants,O;and H;O are promising.Moreover,H;or CO can activate O;to produce H;O;that catalyzes methane partial oxidation more efficiently and selectively than O;or H;O.Therefore,the work of using reducing agent,such as CO and H;have been reviewed,focusing on rational catalyst design that features multifunction(H;O;production and CH;activation).The novel catalyst design has advanced this reaction towards practicality with green oxidants and H;using zeolites-based catalyst.Environmentally friendly zeolite preparation methods and novel two-dimensional(2 D) zeolites that can reduce waste,improve synthesis and catalytical performance substantially are also reviewed in this work to provide insights for a more comprehensive approach to meet the environment protection needs.

A review of crosslinked fracturing fluids prepared with produced water

The rapidly increasing implementations of oilfield technologies such as horizontal wells and multistage hydraulic fracturing,particularly in unconventional formations,have expanded the need for fresh water in many oilfield locations.In the meantime,it is costly for services companies and operators to properly dispose large volumes of produced water,generated annually at about 21 billion barrels in the United States alone.The high operating costs in obtaining fresh water and dealing with produced water have motivated scientists and engineers,especially in recent years,to use produced water in place of fresh water to formulate well treatment fluids.The objective of this brief review is to provide a summary of the up-to-date technologies of reusing oilfield produced water in preparations of a series of crosslinked fluids implemented mainly in hydraulic fracturing operations.The crosslinked fluids formulated with produced water include borate-and metalcrosslinked guar and derivatized guar fluids,as well as other types of crosslinked fluid systems such as crosslinked synthetic polymer fluids and crosslinked derivatized cellulose fluids.The boratecrosslinked guar fluids have been successfully formulated with produced water and used in oilfield operations with bottomhole temperatures up to about 250
F.The produced water sources involved showed total dissolved solids(TDS)up to about 115,000 mg/L and hardness up to about 11,000 mg/L.The metal-crosslinked guar fluids prepared with produced water were successfully used in wells at bottomhole temperatures up to about 250
F,with produced water TDS up to about 300,000 mg/L and hardness up to about 44,000 mg/L.The Zr-crosslinked carboxymethyl hydroxypropyl guar(CMHPG)fluids have been successfully made with produced water and implemented in operations with bottomhole temperatures at about 250t
F,with produced water TDS up to about 280,000 mg/L and hardness up to about 91,000 mg/L.In most of the cases investigated,the produced water involved was either untreated,or the treatments were minimum such as simple filtration without significantly changing the concentrations of monovalent and divalent ions in the water.Due to the compositional similarity(high salinity and hardness)between produced water and seawater,crosslinked fluids formulated with seawater for offshore and onshore jobs were also included.The crosslinked guar and derivatized guar fluids have been successfully formulated with seawater for operations at bottomhole temperatures up to about 300
F.Operating costs have been significantly reduced when produced water or seawater is used to formulate fracturing fluids in place of fresh water.With various challenges and limitations still existing,the paper emphasizes the needs for new developments and further expansion of produced water reuse in oilfield operations.

Verification of two-dimensional LBM-DEM coupling approach and its application in modeling episodic sand production in borehole

The lattice Boltzmann method(LBM)is implemented in the Particle Flow Code(PFC)as a pore-scale CFD module and coupled with the particulate discrete element assemblage in PFC using an immersed boundary scheme.The implementation of LBM and LBM-PFC coupling is validated with the analytical solutions in a couple of hydrodynamics and fluid-particle interaction problems,i.e.,the accuracy of LBM as a CFD solver is verified by solving channel flow driven by a pressure gradient for which the closed-form solution is also derived;the accuracy of LBM-PFC coupling is validated by solving flow across a cylinder,Taylor-Couette flow,K
arm
an vortex street,and fluid flow through a cylinder array.To demonstrate potential applications of this coupling code,a perforation cavity subjected to axial fluid flush is then tested,showing that the collapse and reconstruction of sand arch in the perforation cavity can be reproduced in this coupling system.The developed system is ready for exploring more complicated physical issues involved in sand production.

New insights into hydraulic fracturing fluids used for hightemperature wells

Current interest in deep,low-permeability formations(<10 md)demands accelerated development of high-temperature hydraulic fracturing technologies.Conventional guar systems break down above 300°F and require higher polymer loadings to maintain thermal stability.However,higher polymer loadings generate more residue and damage to the proppant pack and the formation.To resolve these problems,a variety of high-temperature stabilizers are added to enhance the thermal stability of these fracturing fluids at temperatures above 300F.The focus of this work is to:(1)identify those additives that best enhance temperature stability of fracturing fluids and(2)study the rheological influence of incorporating these additives on the fracturing fluid systems.The experimental fracturing-fluid solutions were prepared at a total polymer concentration of 30 and 40 lb/1000 gal.Additives such as synthetic polymer,oxygen scavengers,crosslinkers,crosslinker delay additives,and pH buffers were examined in this work.Hydrated polymer solutions were crosslinked with a metallic crosslinker between 200 and 400°F.Viscosity measurements were carried out in a highpressure/high-temperature(HP/HT)rheometer to evaluate rheology and thermal stability.Results show that adding a synthetic polymer and a crosslinker with the slowest reaction rate improves the fracturing fluid thermal stability.Of the three other additives tested,oxygen scavengers showed the greatest enhancement to thermal stability while pH buffers showed the least.Through the addition of high-temperature stabilizing additives,the fracturing fluid in this work was able to maintain a stable performance at temperatures up to 400°F.Maintaining the thermal stability of fracturing fluids at a lower polymer loading remains a challenge in the industry.This work proposes techniques that can be used to enhance the thermal stability of fracturing fluids.Deeper knowledge about these different techniques will allow for better additive development and application in the field.

Enhanced gelled hydrocarbon well treatment fluids

Compared with water-based well treatment fluid systems,hydrocarbon-based fluids possess advantages such as better fluid compatibility and lower formation damage,especially in water-sensitive formations.Hydrocarbonbased fluids are therefore often used in oilfield operations including hydraulic fracturing,sand control,and coiled tubing cleanout.The metal-crosslinked,phosphate ester-based gelled hydrocarbon(or gelled oil)fluids have been the preferred choice among hydrocarbon-based fluids since they are cost effective,robust at elevated temperatures,and operationally simple as only a couple of fluid additives are involved.Functioning as the gelling agent in gelled oil fluids,phosphate ester could cause fouling in refinery equipment.It is therefore desirable to lower the dosage of the phosphate ester-based gelling agent as much as possible,but without adversely affecting the fluid performance.A number of materials have been identified that could enhance the gelled oil viscosity and stability,which in turn translates into the reduction of the phosphate ester needed in the gelled oil.Among these enhancing materials,a type of aluminum pillared montmorillonite clay(the additive)was found to enhance the gelled oil viscosity to the largest extent.In laboratory tests,30 ppt(30 pounds per thousand gallons)of the additive increased the gelled oil viscosity by 84%(±5%)at 250°F when compared with the baseline gelled oil without the additive.With the additive dosage at 30 ppt,the amount of the phosphate ester in the gelled oil could be reduced by 25%without decreasing the fluid viscosity.The additive was successfully applied to the crude oil-based gelled fluid,resulting in multiple times of viscosity increase in the study.In addition to the gelled oil viscosity enhancement,the additive also increased the regained permeability in the coreflow tests to near 3 times.

Laboratory study on efficiency of three calcium carbonate scale inhibitors in the presence of EOR chemicals

Chemical flooding has been widely used in the oil industry since the 1980s for enhanced oil recovery(EOR)process.Previous studies have shown that the effectiveness of calcium carbonate scale inhibitors is affected by many factors,such as water composition,system pressure,temperature,production rates,pH etc.The breakthrough of the EOR chemicals in the production well could also affect scale formation process and interfere with the scale treatment program as well.However,the studies on the impacts of injected EOR chemicals to scale inhibitor performances are very limited.This paper presents the comprehensive laboratory study on the impacts of the EOR chemicals on CaCO3 scale formation and prevention using static bottle and dynamic tube blocking methods.The EOR chemicals used in this study are a combination of surfactants and polymers.Three different types of inhibitors were evaluated:triphosphonate,penta-phosphonate,and polyacrylate based chemicals.Inhibition(%)from the bottle test and minimum effective dose(MED)based on the tube blocking method were determined for each inhibitor at 160
F.Scale precipitates from the bottle tests were also characterized for morphology and polymorphs using environmental scanning electron(ESEM)and X-ray diffraction(XRD)techniques.Results suggest that the performance of scale inhibitors could be substantially affected by the EOR chemicals.In dynamic tube blocking tests,the MED values of inhibitors were increased roughly 10 times with the EOR chemicals.The static bottle tests showed considerable changes under the test conditions.The impact of EOR chemicals were also demonstrated by the remarkable ranges of crystal morphologies,changing from simple aragonite columns to nanorod,distorted spheroid,and flower-like superstructure in the presence of EOR chemicals and inhibitors.