Processing acoustic data downhole as well as at the surface is necessary to transform the raw acoustic signals recorded by modern logging instruments into data suitable for interpretation and analysis. The goal of acoustic-data processing is to minimize the data noise while maximizing the petrophysical information. Data preprocessing reduces the influences of these sources, thus allowing extraction of the true formation signal. Following the rapid theoretical advances in acoustic-wave propagation made during the 1980s and 1990s, significant advances in data processing provided improved quality in slowness measurements and enabled a number of new applications using Stoneley and dipole-shear wave in open and cased holes. The combined interpretation of Stoneley and dipole-shear acoustic measurements with NMR and borehole imaging enhances formation evaluation.
Vilhena, Odilla (Heriot-Watt University) | Farzaneh, Amir (Heriot-Watt University) | Pola, Jackson (Heriot-Watt University) | March, Rafael (Heriot-Watt University) | Sisson, Adam (Heriot-Watt University) | Sohrabi, Mehran (Heriot-Watt University)
Spontaneous imbibition (SI) experiments in fractured and unfractured Indiana limestone cores were performed to evaluate the impact of fractures in oil recovery. Numerical simulations were run to reproduce the experimental setting and history match fracture and matrix properties. Tracer tests were carried out to investigate the effect of changing stresses in the hydraulic fracture conductivity. The pore space and connected pores in the fractured plug were analysed via Micro-CT scan and thin petrography analysis was carried out to observe the matrix heterogeneity of the samples. Relative permeability, capillary pressure and fracture properties were estimated numerically for Indiana limestone carbonate rocks to match the SI curves measured at a temperature of 58.7 C. The investigation shows that the fractured core has suffered a deformation under stress conditions impacting the initial values of fracture aperture and permeability. This deformation has led to decreased flow rates in the fracture and oil trapping in the fracture channel. At the field scale, this phenomenon could lead to decreased oil recovery in the first days of production.
Fracture propagation (FP) occurs in extensive applications including hydraulic fracturing, underground disposal of liquid waste, CO2 sequestration etc. It is crucial to develop a simulator that is able to reflect physics behind FP and capture the FP path. This work is an extension of the previous developed model (Ren et al. (2018), Ren & Younis (2018)) to the simulation of FP. One of the remarkable benefits using the coupled XFEM-EDFM scheme allows FP free of the remeshing. In this work, the onset of FP is controlled by a single parameter, the equivalent stress intensity factor (SIF). A domain integral method, J integral is applied to extract the SIF information. A time marching scheme is performed to ensure the SIF criterion satisfied everytime fracture propagates. The developed simulator is verified by the analytical solutions and shows the capability of FP simulation in poroelastic materials.
This paper describes the interaction between hydraulic fractures and the multi-porosity system of matrix porosity and natural fracture porosity in shale reservoirs. During the process of hydraulic fracturing, a complex fracture network consisting of primary and secondary hydraulic fractures as well as natural fractures is created. It is postulated that only shale porosities connected with this network will contribute to hydrocarbon production. Furthermore, we propose a way to maximise well productivity by injecting microsized proppants that are less than 150 μm (100 mesh) into the natural fractures and secondary hydraulic fractures to prevent them from closing and thereby increasing the stimulated reservoir volume. The size of the micro-sized proppant should be designed to be between one-seventh and one-third the aperture size of the natural fractures. In addition, various materials for micro-sized proppants are proposed and discussed. Of these, hollow glass microsphere shows more promise because of its light density and track record of being used as an additive material in the oilfield. Although limited laboratory experiments and field tests have shown encouraging results of using micro-sized proppants to enhance the productivity of Barnett shale, more research is warranted to optimize the use of these micro-sized proppants in production enhancement in various shale formations.
Yu, Yanxiang (GOWell International, LLC) | Redfield, William (GOWell International, LLC) | Boggs, Nicholas (GOWell International, LLC) | Qin, Kuang (GOWell International, LLC) | Rourke, Marvin (GOWell International, LLC) | Olson, Jeff (GOWell International, LLC) | Ejike, Mosunmola (Fluor Federal Petroleum Operations)
A new pulsed eddy current (PEC) - electromagnetic (EM) based tool called the enhanced Pipe-thickness Detection Tool (ePDT) has been introduced for multiple pipes' corrosion inspection. The tool can measure the metal wall thickness of five concentric pipes with the maximum outer diameter (OD) up to 26". This capability and ePDT's unique configuration provide the most advanced downhole solution for tubular evaluations of production, injector and gas/oil storage wells. The ePDT features a 2" (51mm) OD with ratings of 350 F (175 C) and 20,000 psi (138Mpa). The innovative sensor of ePDT incorporates: (1) A fractal transmitter (TX) coil array that improves the tool's performances with enhanced signal-to-noise ratio (SNR) covering a wide signal dynamic range, and adaptability for various logging speeds and spatial resolutions for varying pipes; (2) A synthetic aperture of the receiver (RX) coil array for noise compensation from extraneous tool motion; (3) A wide-spatial aperture RX coil array which when combined with (1) and (2) allows for compressing the inner pipe remnant magnetization interferences without sacrificing spatial resolution; (4) A "shallow" measuring transducer to detect EM properties for logging data corrections. The results from lab tests and field trials combined with simulation indicate that the ePDT can quantitatively measure 5 pipes from 2-7/8" as the smallest tubing to the maximum outer casing with the OD of 26". In addition, the logging speed can be significantly increased compared to previous generation tools.
As the number of new exploration and development wells continues to increase, guiding the bit while drilling in real time is becoming one of the most requested technologies. Seismic-while-drilling may enable accurate prediction of high-pressure zones, fractures and cavities, coring points, target depths, and geosteering in high-quality reservoir zones to optimize drilling decisions and reduce costs. A fully integrated real-time system to map and predict ahead of the bit and geosteer in high-quality reservoir zones is presented, showing application of seismic while drilling (SWD). We call this technology DrillCAM.
Recent enabling technological advances were made in wireless high-channel recording, signal enhancement and imaging algorithms, as well as high-performance computational resources that are easily deployable to the field. Such technological advances open a completely new set of possibilities for real-time drill bit guidance and navigation. One key enabler for DrillCAM is the use of wireless seismic receiver stations. Compared to conventional cabled geophones and cableless nodal systems, wireless receivers can provide real-time recording and transmission without the need for extra equipment for data retrieval, flexible receiver spacing and areal coverage. This, in turn, results in a flexible lightweight system for easy mobilization and ultralow power consumption for extended battery life.
We show a carefully designed field data acquisition experiment using the drill bit as a downhole seismic source and a large number of seismic receivers at the surface. The wireless receivers are arranged in flexible geometries that adapt to target bit depths. Using dedicated sensors, the bit signature (pilot signal) is recorded using high-frequency surface and downhole accelerometers. The system integrates surface seismic recordings and surface noise recordings with pilot signal recordings. The initial field experiment is conducted on a nearly vertical onshore well. This experiment demonstrates the feasibility of an integrated DrillCAM SWD system.
The paper presents the motivation, objectives, numerical studies, and first field test of a novel integrated real-time SWD system. Not only does such a system detect bit signals while drilling, it also validates these signals against other measured data and drilling activities.
In past years, the industry has focused on ensuring that cement is efficiently placed in the wellbore and that it does not become mechanically damaged during the life of the well. However, few efforts have been made to determine how cement mechanical integrity (CMI) relates to cement hydraulic integrity (CHI) (i.e., evaluating the flow rate that could occur through the cement barrier), even though CHI is one of the main objectives of placing a cement plug in a wellbore.
The analysis of hydraulic integrity requires that a CMI model be used to compute the state of stress and pore pressure in the cement and to estimate which type of mechanical failure might occur during the life of the well. It also requires that a CHI model be integrated with the CMI model to estimate the rate of fluid that might flow through a cement barrier, should it mechanically fail. This provides the engineer with insight into the long-term integrity of a cement plug.
This paper describes the work conducted on CMI/CHI models for cement plugs, and it presents a sensitivity analysis that demonstrates the value of an integrated CMI/CHI model. The study indicates that (1) well geometry, cement properties, reservoir pressures, cement heat of hydration, and fluid properties are required inputs for proper analysis; (2) the changes of stresses and pore pressure over time need to be computed along the length of the cement plug, with sensitivity analysis to consider the existing uncertainties; (3) a cement plug might preserve its sealing capability, even if the CMI model shows the existence of a microannulus (e.g., when the fluid viscosity is very high); and (4) a cement plug might lose its sealing capacity, even if the CMI model shows no induced defect (e.g., when a microannulus is propagated as a hydraulic fracture).
These last two observations are important because they show that what a CMI model cannot predict, a CHI model can.
Szymczak, Piotr (Faculty of Physics, University of Warsaw) | Kwiatkowski, Kamil (Faculty of Physics, University of Warsaw) | Jarosinskí, Marek (Polish Geological Institute) | Kwiatkowski, Tomasz (National Centre for Nuclear Research) | Osselin, Florian (University of Warsaw and University of Calgary)
Piotr Szymczak and Kamil Kwiatkowski, Faculty of Physics, University of Warsaw; Marek Jarosinskí, Polish Geological Institute; Tomasz Kwiatkowski, National Centre for Nuclear Research; and Florian Osselin, University of Warsaw and University of Calgary Summary A relatively large number of calcite-cemented fractures are present in gas-bearing shale formations. During hydraulic fracturing, some of these fractures will be reactivated and may become important flow paths in the resulting stimulated fracture network. On the other hand, the presence of carbonate lamina on fracture surfaces will have a hindering effect on the transport of shale gas from the matrix toward the wellbore. We investigate numerically the effect of lowpH reactive fluids on such fractures, and show that dissolution of the cement proceeds in a highly nonuniform manner. The morphology of the emerging flow paths ("wormholes") strongly depends on the thickness of the calcite layer. For thick carbonate layers, a hierarchical, fractal pattern appears, with highly branched wormhole-like channels competing for an available flow. For thin layers, the pattern is much more diffuse, with less-pronounced wormholes that merge easily with each other. Finally, for intermediate thicknesses, we observe a strong attraction between shorter and longer wormholes, which leads to the formation of islands of carbonate lamina surrounded by the dissolved regions. We argue that the wormholeformation processes are not only important for the increase of shale-gas recovery, but also can be used for retaining the fracture permeability, even in the absence of proppant. Introduction The occurrence of natural fractures in shale rocks has been reported across a number of different formations in the United States (Curtis 2002; Gale et al. 2007; Gale et al. 2014; Gasparrini et al. 2014) and worldwide (Imber et al. 2014). Depending on the geological characteristics of the formations and their burial histories, natural fractures can be either open or be cemented with a different degree of sealing, from thin calcite lamina covering fracture surfaces to the fully, or almost fully, sealed veins (Curtis 2002; Asef and Farrokhrouz 2013; Gale et al. 2014). The presence of natural fractures and their impact on hydraulic fracturing and on gas production have been the subject of numerous studies (Gale et al. 2007, 2014; Walton and McLennan 2013; Li 2014).
Huang, Jixiang (Lawrence Livermore National Laboratory) | Fu, Pengcheng (Lawrence Livermore National Laboratory) | Hao, Yue (Lawrence Livermore National Laboratory) | Morris, Joseph (Lawrence Livermore National Laboratory) | Settgast, Randolph (Lawrence Livermore National Laboratory) | Ryerson, Frederick (Lawrence Livermore National Laboratory)
Reservoir depletion and its influence on subsequent hydraulic fracture propagation are studied using a three-dimensional fully coupled geomechanics, fluid flow and hydraulic fracturing code. Pressure change and resultant stress alteration are captured through a rigorously developed poroelastic model, validated against analytical solutions. In the context of parent-child well interference, depletion-induced stress reduction will attract fracturing from nearby wells, unfavorably affecting production of the parent well in most cases by leaving the target region unstimulated or understimulated. One engineering practice to remedy this impact is to refracture the parent well before fracturing in child wells. How this treatment impacts the fracturing and to what extent it can prevent the attraction have been quantitatively studied using the geomechanics-flow coupling and hydraulic fracturing capabilities within a unified framework. Sensitivity studies of matrix permeability, production time and fracture spacing have been performed to explore the feasibility of controlled fracture growth into a depletion region. The amount of fluid required to refracture the producing well sufficiently to create a stress barrier that inhibits deletarious growth of child fractures depends on the degree of reservoir depletion. A complex scenario involving the interactions between reservoir depletion, refracturing and geologic factors such as stress barriers is also studied. The possibility for a subsequent fracturing to break through a stress barrier after a certain time of production, which would otherwise be impossible, is explored, indicating a potential parent-child well interference mechanism even when the parent and child wells are located in different formations. This phenomenon is essentially three dimensional and has not been captured by previous studies.