Development of source-rock resources relies on the rigorous knowledge of their petrophysical properties such as porosity, permeability, and hydrocarbon saturation. In parallel, a concise description of the wettability and pore structures is commended. This paper presents a detailed Nuclear Magnetic Resonance (NMR) T2 study of the wetting characteristics and pore structure in organic-rich source rocks from different locations including the Eagle Ford formation. Although these rocks are highly laminated and calcite dominated, our studies indicated that they have distinct different pore structure and connectivity, and differ in how TOC is dispersed within the rock fabric. We believe that the entailed findings could influence our thinking on how best to produce these shales, wellbore stability, drilling fluid selection and other asset development actions.
Source-rock samples with varied amount of total organic content (TOC) were drilled perpendicular or parallel to the laminations. The samples were cut into twin plugs which were sequentially saturated by spontaneous imbibition of 5% KCl brine and diesel (oil). The NMR T2 measurements were used to determine the fluid imbibition rate and amount, as well as the porosity associated with organic and inorganic components of the source rocks. The fracture apertures were obtained via an application of characteristic T2 cutoff times to the NMR T2 distributions. The mineral elements, phases and TOC of the rocks were measured using X-ray Fluorescence (XRF), X-ray Diffraction (XRD) and HAWK pyrolysis, respectively.
The prevalence of surface relaxation on the NMR dynamics was prominent as the transverse relaxation took place at time scales (T2 ≤ 100 ms) much shorter than their bulk values. The overall wettability of the samples showed a mixed character as the brine and the oil had been intimately imbibed. Nevertheless, the details of the wetting behavior of the Eagle ford samples and the other samples were different. For instance, Eagle Ford samples imbibed larger volumes of brine and faster than oil, on the contrary the other samples imbibed larger volumes of oil and faster than brine.
The apparent preference of oil on the other samples is attributed to their high TOC compared to the Eagle Ford samples. Upon imbibition in these samples, brine is observed to flow along the clay rich bedding planes. In fact, the interaction between brine and clay is identified to be the potential driver of the rock stability problems especially near the wellbore; however it is constrained by the type of residing clays. The discrepancies in the wetting traits are magnified by the presence of fractures which enhanced the network connectivity of both hydrophobic and hydrophilic pores or even across them. Furthermore, the fractures allowed the fluids to surpass the vertical bedding planes and thus accelerating the fluid distribution processes inside the pore space. The fracture apertures were found to range from 1 μm to 15 μm which are typical values for source rocks (
The recent crash in the oil market has allowed the industry to reduce the pace of evaluation and completion decisions in unconventional reservoirs, and turn to a more science-based decision-making process for project execution. The traditional stimulation design based on the geometric spacing of induced fractures is now gradually changing to geological spacing (i.e., a design based on an understanding of the reservoir geology) to enhance hydraulic fracture stimulation effectiveness for drastically reduced cost. A methodical rock texture characterization of core samples and cuttings can provide powerful information that can be used reliably and cost-effectively to optimize fracture stimulation designs by placing frac stages based on rock characteristics. This paper presents a new method to quantify rock texture based on automated petrographic analysis that uses advanced microscopy image analysis from scanning electron microscopy (SEM) and optical microscopy. A procedure called "quantitative evaluation of minerals using a scanning electron microscope" (QEMSCAN) and optical microscopy analyses were used to image rock samples prepared from cores and cuttings. Rock texture parameters were extracted automatically using new digital data processing techniques. The information from automated petrographic analysis was used to determine the spatial distribution of all components including mineral composition, framework grains, matrix, cement, grain size and shape, pore size and shape, modes of contact between grains and the nature of porosity. The results showed that while mineral composition of rock is important, texture characterization is far more significant to understand rock behavior than has been reported in the industry. Our results demonstrate the importance of quantitative microscopy and how it can provide an understanding of the key relationship between rock texture and rock behavior.
A new method was produced to characterize rock texture quantitatively from advanced image analysis with the aid of an automated petrographic system.
Crane, Davon (Continental Resources) | Zhang, Youhe (Schlumberger) | Douglas, Charles (Schlumberger) | Song, Huimin (Schlumberger) | Gan, Xiaoge (Schlumberger) | Lin, Zhijun (Schlumberger) | Mueller, Levi (Schlumberger) | Skoff, Greg (Schlumberger) | Self, Jordan (Schlumberger) | Krough, Bradley (Schlumberger)
Most traditional polycrystalline diamond compact (PDC) cutting elements have a flat polycrystalline diamond table at the end of cylindrically shaped tungsten carbide body. During drilling, the flat diamond table engages the formation and shears the rock layer by layer. A new ridge-shaped diamond cutting element (RDE) has a similar cylindrical tungsten carbide base; however, the diamond table is shaped like a saddle with an elongated ridge running through the center of the diamond table and normal to the cutter axis. The intended cutting portion, the "ridge," engages the formation to fracture and shear the rock at the same time. The design intent was to create a unique cutting element that could combine the crush action of a traditional roller cone insert and the shearing action of a conventional PDC cutter. The new cutting elements were tested in the laboratory against standard flat PDC cutters in a rock-cutting evaluation, and later the new elements were applied to PDC bits and run under real drilling conditions.
The laboratory rock-scrape tests indicated that the new cutting element not only enables the cutter to efficiently shear formation in the same way as a conventional PDC cutter, but also delivers a crushing action similar to a roller cone insert. Preliminary results indicated a reduction of roughly 40% in both cutting force and vertical force on the new ridged diamond element cutters (RDE) over a conventional PDC cutter. Similar findings were also observed during the rock-shearing test on a vertical turret lathe (VTL). Subsequent field tests in multiple areas in North America have produced faster rates of penetration (ROP) in most of the cases. The trials indicate that the new cutting element is efficient at removing rock, and a bit equipped with these elements requires less mechanical specific energy (MSE) during drilling than does a bit with a conventional PDC cutter. In addition, the reduced cutting forces reduces bit torque and thus improves the drilling tools’ life and the bit directional performance. Field data has proven this technology improves drilling performance in terms of ROP and footage over the current PDC bits fitted with traditional flat PDC cutters.
Alkamil, Ethar H. K. (University of Basrah, Missouri University of Science and Technology) | Abbood, Husam R. (Missouri University of Science and Technology) | Flori, Ralph E. (Missouri University of Science and Technology) | Eckert, Andreas (Missouri University of Science and Technology)
During drilling operations for the E oilfield in the Mishrif formation in southern Iraq, stuck pipe has been identified as a significant geomechanical problem for several wells. In this study, a 1-D mechanical earth model (MEM) of the Mishrif formation is compiled based on its state of stress and rock strength parameters and is utilized to assess the contribution of borehole collapse leading to the stuck pipe problems.
The MEM model is based on the principal in situ stresses and their orientation obtained from wireline logs measurements, measuring while drilling (MWD), and leak off test (LOT). Rock strength properties are obtained from empirical equations and extended leak off tests. The in situ stresses are transformed to calculate and analyze mud pressure conditions for all wellbore azimuths and inclinations. Two different failure criteria (the Mohr-Coulomb and Mogi-Coulomb rock failure criteria) are used in order to determine feasible drilling trajectories (with respect to the σH orientation) and mud pressure conditions for several wells.
This work was conducted to study the behavior of the collapse pressure for Mishrif formation under a normal faulting (NF) in situ stress regime. The results of this study show that wells characterized by stuck pipe are drilled along azimuths which promote wellbore collapse. Based on the MEM results, the mud pressure window is calculated, and stable azimuths and inclinations for each well are suggested. If a specific azimuth for a well cannot be altered, an optimum inclination is recommended to reduce the severity of the borehole collapse. This study based on a 1-D MEM model for directional drilling can improve the well drilling efficiency by reducing non-productive time due to the wellbore instability.
ABSTRACT: The failure mechanism of haulage gate surrounding rock in 402103 fully-mechanized top-coal caving face of some deep coal mines of Bin-Chang Mining Region in Shan-xi province are studied. The results show that haulage gate surrounding rock in deep coal mine has the characteristics of big deformation, asymmetry stress distribution of surrounding rock complex. Based on the support idea, which is first pressure released, second pressure relief, third anti-pressure, support and on-site monitoring program for haulage gate in 402103 fully-mechanized top-coal caving face is carried out. The practice shows that the design support parameters of crossheading are reasonable, and the supporting effect meets the needs of safety production.
With the increase of the mining depth, geological environment becomes more complex; the roadway surrounding rock shows characteristics of large deformation, high stress and sustainable creep, and the risk of roadway rock burst has been increased greatly. At the same time, deep roadway is influenced by high temperature, high confining pressure and high pore pressures; Deformation of the surrounding rock in roadway shows new characteristics that are different from shallow tunnel.
Domestic and international scholars have conducted extensive research on the issue of deep roadway support (He et al. 2007, Kang et al. 2010, N. Zhang et al. 2009, Bai et al. 2007). But the research on the issue of roadway support in special thickness coal of deeply buried coal mine was relatively less.
In order to ensure the safety of construction, the research on the issue of roadway support in special thickness coal of deep buried coal mine is necessitated; we should put forward reasonable and feasible supporting solutions, and provides a reference for other roadway support of deep buried coal mines in the west. Take the support problem in concern, a support scheme is proposed and engineering practice and deformation monitoring are carried out.
Lian, C. J. (Shandong University of Science and Technology) | Hou, J. Z. (Shandong University of Science and Technology) | Gao, G. L. (Taian Taishuo Strata Control Science and Technology Co. Ltd.) | Wang, G. (Taian Taishuo Strata Control Science and Technology Co. Ltd.) | Song, W. T. (Henan Polytechnic University)
ABSTRACT: It has wide distributions and large recoverable reserves of Jurassic period coal seam in China. It is difficult to maintain stability of the development roadways with long service term for Jurassic strata because there are abundant argillaceous rocks and some minerals in the high argillaceous rocks will be expanding while meeting with water. The fractures of the roadways develop well under high stress and are suitable to filling with grouting. But the poor cementing performance of cement with argillaceous rock as well as a heavy water filtration rate of cement slurry had resulted in failures of many engineering cases adopting cement grouting to reinforce this kind of roadways. In this paper, according to characters of the high argillaceous rock in Jurassic strata, a marlaceous inorganic grouting material which possesses the well cementing performance with argillaceous rocks and little filtration rate was introduced; and the grouting reinforcement mechanism, construction technique and engineering application effect about it was clarified. It will be of great significance for reinforcement and maintenance of the development roadways with high argillaceous rocks.
According to statistics, 60% of the proved coal reserves in China distributes in Early-Middle Jurassic period of northern North China, southern Northeast China and Northwest China, along with late Jurassic to early Cretaceous period of Northeast China and east Inner Mongolia. The period of coal forming is short and argillaceous rocks are abundant in Jurassic strata. Moreover, there are quite a few expanded minerals in some strata. So the roadways are easily to be deformed and damaged when affected by mining-induced stress. In addition, this kind of soft rock roadways has an obvious time effect. For the development roadways with long service term, serious deformations are frequently observed and part of the roadways has suffered deformation and maintenance time after time. The stability support of the development roadways really need much cost.
ABSTRACT: The vertical stress, failure patterns and deformation of roadway surrounding rock under different coal pillar width are studied by using FLAC3D software. The results show that with the increase in the width of coal pillar, stress concentration range and factor in pillar decreases, gradually showed uniform bearing form, at the same time, the displacement of roadway and plastic zones in pillar gradually decrease. With the increase of the width of coal pillar, the range of elastic core is larger, indicating that the more stable the roadway coal pillar is, the more safety will be. Taking into account that large coal pillar width would result in the waste of resources, the reasonable coal pillar width is between 14-16 m.
According to numerous studies on the rational section coal pillar, many effective methods to determine the reasonable size of coal pillars can be categorized as follows (Cui et al. 2012, Tu et al. 2011, Zhang & Shi 2004, Chen 2014, Shao et al. 2014): 1) Mathematical statistics, a large number of measured results give rise to inductive reasoning that unstable surrounding rock conditions of coal pillar size; 2) Application of mine pressure regularity with various coal pillar and empirical formula to analyze the reasonable size of the coal pillar; 3) The reasonable coal pillar width range determined based on measured pillar abutment pressure distribution method analysis of coal seam; 4) According to the limit equilibrium theory to derive the coal hold steady when the width formula; 5) The estimation formula of three dimensional plastic zone width of coal pillar stress. The numerical simulation of roadway surrounding rock is performed to analyze the width of coal pillar under different stress and movement for working face 222203 in Shuangxin Mining Co. coal mine, Inner Mongolia.
ABSTRACT: Inverse analysis is commonly used in identifying geomechanical parameters based on the monitored information such as displacement or stress. Conventional inverse analysis method is incapable of recognizing non-linear relationship involving displacement, stress and mechanical parameters effectively. A hybrid model which combined Multi-output-Support Vector Machine (MSVM), Artificial Bee Colony (ABC) and numerical analysis has been proposed to estimate the in situ stress and rock mechanical parameters based on borehole fluid pressure. MSVM is used to represent the non-linear relationship between parameters of numerical model and borehole fluid pressure. ABC is used to search the set of unknown recognized parameters based on the objective function. Numerical analysis of hydraulic fracturing is used to create the necessary training and testing samples for the hybrid MSVM-ABC model. Results of numerical experiments demonstrate that a hybrid MSVM-ABC model for inverse analysis can effectively identify in situ stress and rock mechanical parameters based on wellbore fluid pressure in the hydraulic fracturing process.
Geomechanical parameters such as Young's modulus and in situ stress in the field of petroleum are important to reservoir simulation, borehole stability analysis and production of petroleum (Gokceoglu et al. 2004, Juliusson 2012). However, it is difficult to obtain those parameters accurately and efficiently using the traditional laboratory test and in-situ test because of the complex, nonlinear and uncertainty of rock mass characters (Zhao & Yin 2009). Inverse analysis method provides a good way to get these parameters by combining the field-observed information with numerical simulation. Inverse analysis are commonly used in rock mechanics and engineering such as tunnel, underground engineering and rock slope etc (Sakurai & Takeuchi 1983, Gioda & Maier 1980, Miranda et al. 2011, Feng & Hudson 2011).
In the petroleum industry, hydraulic fracturing is the most common technique to perform well stimulation and earth stress characterization of hydrocarbon reservoirs, especially for unconventional reservoirs such as shale gas, tight gas and coal bed methane. In this paper, geomechanical parameters were estimated by combining inverse analysis and hydraulic fracturing test.
Energy demand has been escalating and is predicted to increase further in the coming decades. The dialogue on global climate change has the world abuzz on the primary green house gas, carbon dioxide. Both of these factors have created a perfect storm for the use of carbon dioxide for enhanced oil recovery. The petroleum industry is ideally suited for disposing of this green house gas. Each oil company (and others) has therefore stepped up its efforts in carbon dioxide utilization, either for EOR or sequestration. The injection of CO2 into a reservoir is not new. Indeed CO2 injection has established itself as a very efficient mechanism for increasing oil recovery.
To design a CO2-EOR or CO2 sequestration project, one requires a large set of appropriate experimental data for a given reservoir/fluid system. Where does one start? Even if the data have to be generated in a service lab, a good design requires some thought and effort. A search of the literature reveals no best practices for generating this dataset. This paper presents a comprehensive experimental design for conducting a CO2 laboratory study.
The essential components of a laboratory study for CO2 injection include measuring fluid-fluid interactions and fluid-rock interactions. Fluid-fluid studies include miscible displacement tests, measurement of minimum miscibility pressures, fluid properties of CO2-oil or CO2-brine mixtures including viscosity and density, asphaltene precipitation, and swelling. Fluid-rock interaction studies typically include coreflooding tests for determining the oil recovery potential, three-phase relative permeability, critical gas saturation, gas trapping and wettability changes. Each of these sets of experiments will be described in light of their best practice. The ultimate goal is to establish a procedure for generating a reliable and accurate dataset.