Globally, most oil fields are on the decline and further production from these fields is addressed to be practical in cost-effectiveness and oil productivity. Most oil companies are adopting two main technologies to address this: artificial intelligence and enhanced oil recovery (EOR). But the cost of some of these EOR methodologies and their subsequent environmental impact is daunting. Herein, the environmental and economic advantage of microbial enhanced oil recovery (MEOR) makes it the point of interest. Since, there is no need to change much-invested technology and infrastructure, amidst complex geology during MEOR application, it is entrusted that MEOR would be the go-to technology for the sustainability of mature fields.
Despite the benefits of MEOR, the absence of a practical numerical simulator for MEOR halts its economic validation and field applicability. Hence, we address this by performing both core and field- scale simulations of MEOR comparing conventional waterflooding. The field scale is a sector model(fluvial sandstone reservoir with 13,440 active grid cells) of a field in Asia - Pacific.
Here we show that pre-flush inorganic ions (Na+ and Ca2+) affect the mineralization of secondary minerals which influences microbe growth. This further influences carboxylation, which is relevant for oil biodegradation. Also, as per the sensitivity analysis: capillary number, residual oil saturation and relative permeability mainly affect MEOR. Secondary oil recovery assessment showed an incremental 6% OOIP for MEOR comparing conventional water flooding. Also, tertiary MEOR application increased the oil recovery by about 4% OOIP over conventional water flooding. It was established that during tertiary recovery, initiating MEOR after 5years of conventional waterflooding is more advantageous contrasting 10 and 15years. Lastly, per probabilistic estimation, MEOR could sustain already water-flooded wells for a set period, say, a 20% frequency of increasing oil recovery by above 20% for 2 additional years as highlighted in this study.
Investigation of the effectiveness of matrix stimulation treatments for removing drilling induced damage in Akita region in northern Japan is of interest due to the presence of large quantities of acid-sensitive minerals, such as analcime. Feasibility study of the sub-commercial field redevelopment in the Kita-Akita oil field, one of the satellite fields of main Yabase oil fields, which produced from 1957 to 1973, and were plugged and abandoned, were conducted. As a part of the studies, matrix acidizing laboratory experiments were performed. Conventional mud acids and formic-based organic mud acid systems cause significant permeability damage due to instability of analcime in these acids. This study focuses on the development of a treatment fluid that removes drilling-induced damage and is also compatible with the formation.
Petrology studies and core flow tests were used in conjunction with geochemical modeling to achieve this objective. A petrographic analysis on the untreated cores showed abundant tuffaceous pore-filling mineral phases, ranging from 12 to 20% in volume. Smectite clay and microcrystalline quartz are the major constituents as alteration products of volcanic glass. Analcime was present in significant quantities in all samples tested.
Six core flow tests were performed on formation cores to optimize the acid preflush and main acid stage. Permeability change due to the treatment fluids was recorded for the tests. Chemical analysis of the effluent was performed on three core flow tests. Core samples before and after acidization were characterized based on thin section, X-ray diffraction (XRD), scanning electron microscopy(SEM) and mineral mapping.
Core flow tests with a conventional retarded organic mud acid resulted in only a 75% retained permeability. The permeability damage by the retarded organic mud acid was surprising because it usually performs well in acid-sensitive formations. A chelant based retarded mud acid was tested next and resulted in minor formation damage. It can potentially be used in a field treatment as its high dissolving power is expected to more than compensate for the damage. The highest retained permeability was obtained with an acetic-HF acid system. It was successfully able to remove drilling-induced damage and was also compatible with the native mineralogy. Core flow tests were used to calibrate permeability-porosity relationship used in the geochemical simulator. The geochemical simulator was then used to predict field-level acid response.
The analytic methods presented are general enough to be of interest to sandstone acidizing studies where detailed analysis is needed for damage identification and removal. The fluids developed for this formation area good candidates for other formations where conventional acid systems have not performed well. This study also highlights close collaboration between an operator and service company to find a workable solution to a challenging stimulation requirement.
Ueda, Kenji (INPEX Corporation) | Ono, Kenya (INPEX Corporation) | Fuse, Kei (INPEX Corporation) | Nonoue, Ayako (INPEX Corporation) | Furui, Kenji (Waseda University) | Mustapha, Hussein (Schlumberger) | Tsusaka, Kimikazu (INPEX Corporation) | Furuta, Kohei (INPEX Corporation) | Rodriguez-Herrera, Adrian (Schlumberger) | Makimura, Dai (Schlumberger) | Manai, Taoufik (Schlumberger) | Ito, Toru (INPEX Corporation)
The legacy of conventional fields has resulted in many low permeability reservoirs deemed sub-commercial without an appropriate stimulation strategy. With low permeabilities and potentially heterogeneous reservoir characteristics, an optimal development approach would highly depend on their specific reservoir properties that may well require stimulation methods other than hydraulic fracturing. In this paper, we present a fully integrated characterization and modeling workflow applied to the Kita-Akita oil field in northern Japan, demonstrating the screening process for multiple completion and stimulation methods in a highly heterogeneous, low permeability sandstone reservoir.
To select a best completion and stimulation candidate from multiple methods, we constructed an evaluation matrix including the maturity of technologies, applicability to our reservoir, productivity, and economics. Multi-branch type completions such as radial drilling and fishbone drilling, as well as hydraulic fracturing were simulated and subsequently compared based on their productivities. Especially for the radial drilling and the fishbone drilling, a 3D FEM model was built for their complex laterals, and the inflow performances were evaluated with homogenous reservoir properties, respectively. Besides, due to the highly heterogeneous nature of the reservoir, we built a full-physics subsurface model based on a pilot-hole data acquisition and legacy 2D seismic lines. The 3D model served as a canvas to assess reservoir flow and geomechanical behavior, calibrated with production history from past producing wells in the 1950's to 1970's. Based on these models, the best infill drilling location was selected and multiple well completion and stimulation practices were evaluated.
Through the screening methodology, the multi-stage hydraulic fracturing was identified as the best suited from an instantaneous productivity perspective. Yet, even though hydraulic fracturing would enhance the accessibility into multiple distinctively isolated sandstones occurring in the deepwater slope channel setting, the treatment costs exceeded the economic threshold significantly in our case. Inflow performance evaluation based on the 3D FEM modeling illustrates multi-branch type completions such as radial drilling and fishbone drilling were identified with a good stimulation skin factor. As a result of 3D simulation study, multi-branch completion was revealed as a technical and economically viable stimulation option in the heterogeneously distributed sandstone reservoirs.
The advent of recent completion and stimulation techniques now renders low permeability reservoirs with relatively large development potential. Even with the development challenges quite different from conventional reservoirs, the approach shown in this paper provides a helpful reference for the study and decision-making process when the legacy field needs an optimal stimulation strategy.
As this editorial goes to press, a constructive debate is happening over the unconventional-resource renaissance in Colorado. Each side held firmly to their respective corners until a compromise was brokered by Gov. John Hickenlooper, who also is a geologist and beer brewer. This deal moved the conversation from an emotionally charged political venue and put it in a more-objective, multifaceted stakeholder commission. Colorado has a bountiful resource base. Unconventional resources are more common than conventional; thousands of fracture jobs lead to refracturing; and the oil-and-gas-industry gross domestic product rivals that of construction or the food and lodging industries.
To better define the accumulations of gas hydrates and free gases in the Kumano forearc basin which is located above accretionary prism in the Nankai margin off the Kii peninsula, Japan, we performed a high-resolution seismic velocity analysis to 3D seismic data using the method of conventional semblance spectra via automatic velocity picking algorithm. The results revealed that gas hydrate-bearing sediments above bottom-simulating reflector (BSR) and free gas-bearing sediments below BSR are characterized by P-wave velocities of 1900 – 2500 m/s, and 1000 – 1800 m/s, respectively. Gas hydrates are highly concentrated around the rim of the outer ridge where faults are densely developed, whereas free gas reservoirs are widely distributed below BSRs and are considerably high above ridge topography, which is considered as a structural trap for gas reservoirs. Then, the velocity model was converted into a gas hydrate and free gas saturation model using Archie’s equations and rock physics models. The results indicated that saturation of gas hydrates and free gases ranges from 0 to 50% and 0- 20% in the pore space, respectively. In addition, based on the velocity model of gas hydrates and free gas distribution, we suggested that gas hydrates concentrated due to the free gas influx which migrated upward through steeply dipping strata and faults or fractures cutting through the basin. Therefore, these factors generated by intensive tectonic movements in the plate subduction zone controlled the distribution and saturation pattern of gas hydrate and free gas formations.
Gas hydrates, crystalline solids like ice bonding both water and gas molecules, occur in the permafrost region and deep water sediments where are high pressure and low temperature condition. (Kvenvolden, 1993; Sloan and Koh, 2007). They are potentially unconventional resources and contribute to global climate change and potential drilling hazards (Ruppel and Kessler, 2017).
Yamashita, Yoshihiro (OYO Corporation) | Oda, Yusuke (OYO Corporation) | Sakashita, Susumu (OYO Corporation) | Groom, Douglas (Geome) | Wang, Fei (Geometrics Inc.) | Echigo, Tomoo (Geo-Research Institute) | Kagohara, Kyoko (Yamaguchi Univ.) | Okada, Shinsuke (IRIDeS, Tohoku Univ.) | Kosaka, Hideki (Kankyo-Chisitsu Corporation) | Miyauchi, Takahiro (Graduate School of Science Chiba Univ.) | Imaizumi, Toshifumi (Graduate School of Science Tohoku Univ.)
We conducted a high-density arrayed CSAMT survey to delineate active fault in the eastern foot of Tsugaru Mountains in Japan. The survey purpose is to delineate subsurface structure of this area including blind thrust as materials of predicting the magnitude of an earth quake. In this area, the seismic reflection survey was conducted. The CSAMT survey line was a part of seismic survey line and the length was 4.6 km. We set 93 scalar measurement stations at intervals of 50 m so as to be able to capture steep structures. We used Geode EM3D as receivers and GeoTx20 as a transmitter, manufactured by Geometrics. Geode EM3D receiver is multi-channel and distributed EM survey instruments. We set 6 receivers array at maximum. Each receiver can collect 3 scalar measurements of adjacent stations. Hence we can acquire 18 stations during a procedure of transmitting 33 kinds of frequencies from 0.125 Hz to 8192 Hz. Such array CSAMT measurement contributed to improve measurement efficiency. The result of resistivity section clearly presents a gap of low resistivity zone. From integrated interpretation with seismic reflection, we concluded that the gap of low resistivity structure seems to be caused by blind thrust.
Presentation Date: Wednesday, September 27, 2017
Start Time: 3:55 PM
Location: Exhibit Hall C, E-P Station 2
Presentation Type: EPOSTER
In this study, pore structures and water permeation property of a shale rock are analyzed by means of X-ray CT. The target samples are produced Kushiro district in Hokkaido, Japan. Underground of this area is consisted by Cretaceous formation. Firstly, one dimensional permeation tests were performed by using core sample retrieved from Cretaceous formation, and intrinsic permeability was evaluated. Secondly, the internal structure of rock samples was observed by X-ray CT scanner, and porosity distributions were also evaluated by comparing CT image data between the dry and the water-saturated conditions. It was found that Cretaceous formation has relatively low permeability as k=10−19 ~ 10−18 m2. It was also found that the porosity of each sample was approximately 7%~13%, however, porosity distribution was not uniform, and was strongly influenced by density distribution in samples.
Natural gas/oil has been developed all over the world, and most of gas/oil has been supplied from so called conventional natural gas/oil deposits for long time. However, as technology and geological knowledge is advancing, many unconventional natural gas/oil deposits have been discovered, and total amount of supplied energy is increasing . The representative of unconventional natural energy deposits is shale rock layers . In Japan also, there are several promising shale rock layers as gas/oil reservoirs , and certain amount of gas/oil deposits are inspected.
In this study, pore structures and water permeation property of a shale rock are analyzed by means of X-ray CT. The target samples are produced Kushiro district in Hokkaido, Japan. Underground of this area is consisted by Cretaceous formation. This is mainly formed by sandy shale and it is spreading under Kushiro coal seam. It is estimated that huge amount of methane gas exists in the Cretaceous formation , however, the origin of the methane and the storage process in the formation including its total amount are still not clear. The purpose of this study is to obtain fundamental characteristics or properties of the shale rocks located at Kushiro, such as nominal porosity, permeability, porosity and density distributions. Here, nominal porosity is evaluated through water absorption tests. One dimensional permeation tests are performed, and intrinsic permeability of the shale samples are evaluated. In order to inspect the internal structure of the shale, X-ray CT method is applied. From the CT image data, the internal structure of rock samples is discussed, and porosity distributions are also evaluated by comparing CT image data between the dry and the water-saturated conditions.
Although many gas extractors and detectors currently exist, there is no significant comparison between the data quality that they produce. Most advances in mud-gas interpretation and deployable new technologies were driven by service companies' needs to provide operators with the highest standards of data and interpretation while using their most cost-effective systems for mud-gas analysis. This led to rapid growth in the mud logging sector for providing more scientifically rigorous services at the rigsite. Each new method provided a suite of applications and, more importantly, limitations; a comparison study was performed to gather this information.
The comparison study focused on quantitative gas measurement (QGM), constant volume (CV), and constant volume and temperature (CVT) extractors with gas chromatographs (GC) and mass spectrometers (MSs). These systems were compared by operating them simultaneously at the rigsite.
The CVT system with MS outperformed all other systems. The QGM and CV gas extractors lacked the consistency observed in the CVT system, and the QGM and CV extractors failed to consistently extract C3+ components from the drilling fluid. The MS on the QGM and CV systems added limited value resulting from using atmospheric air as the carrier gas and the lack of a constant temperature. Although the installation of the CVT is more costly and time consuming, these issues are offset by the additional information and consistency provided by the CVT.
Comparing the three extraction systems with two different gas detectors helped determine the best solution on a cost and necessary information basis.
With increased costs associated with drilling a well, more accurate geochemical data is expected, which helps reduce drilling costs through optimization of downhole sampling using logging while drilling (LWD) and wireline. To produce this better understanding of the reservoir, the oilfield sciences have developed a broader understanding of gas extraction and detection from drilling fluids. This has led to the development of more complex extraction methods, from the traditional agitated extractor with uncontrolled fluid flow rates and temperatures to complex temperature, pressure, and flow-controlled extraction methods with automated controls. For analytical analysis, the need for more accurate data with greater speciation has driven the development of more complex field-deployable analytical instrumentation, resulting in a shift from a basic total hydrocarbon analyzer to complex MSs. The development of more complex equipment has resulted in increased equipment costs and the need to justify the cost of surface equipment with the replacement of downhole equipment.
In this study, we propose a new approach to estimate depth-dependent stress field in a borehole instead of conventional in-situ measurement methods. Seismic interferometry and Alford rotation methods are used to obtain S-wave anisotropy as a proxy of stress field. Ambient noise records observed by horizontal components of vertical seismic array system installed in a borehole were used as input data. We first calculate virtual cross dipole seismic records by seismic interferometry method applied to the observed continuous ambient noise records. Then we applied the Alford rotation and layer stripping technique to obtain depthdependent S-wave anisotropy parameters, i.e., the orientation of fast S-wave and the difference between fast and slow S-wave velocities of formations along the vertical axis of a borehole. Obtained results, the orientation of fast S-wave, have very good agreement with directions of principal horizontal stress, which was revealed in the analysis of borehole breakout just after drilling the borehole. We propose that our approach would readily be applied to monitor the stress field around a borehole instead of conventional insitu measurement methods.
In a crustal-scale marine seismic survey with sparsely deployed ocean bottom seismographs (OBS), spatially continuous imaging with primary reflections is difficult for shallow reflectors, because the imaging area is limited to beneath each OBS. In order to obtain continuous reflection image along the whole survey line, seismic interferometry is a useful method to utilize the surface-related multiple reflection signals. In this study, image domain seismic interferometry is proposed as a direct imaging method of multiple reflections based on a reverse time migration principle. Compared to the general data domain seismic interferometry, synthesizing of the virtual source data for redatuming is not necessary before imaging, and the redatuming and the imaging are done simultaneously. The verification test of the image domain interferometry by applying to the OBS survey data in Nankai trough shows good result to obtain the continuous reflection image from sparse receivers and dense airgun shots. The direct depth migration technique will be useful for full wavefield imaging in the OBS survey by integrating the primary reflections and the multiple reflections.
Presentation Date: Tuesday, October 18, 2016
Start Time: 3:45:00 PM
Presentation Type: ORAL