Search citation statements
Paper Sections
Citation Types
Year Published
Publication Types
Relationship
Authors
Journals
INTRODUCTIONTraditionally, measurements in oil & gas industry have inverse relation between formation vertical resolution and spatial coverage. The logs provide hi-resolution information but close to the wellbore while surface based measurements such as seismic & gravity provide field wide spatial coverage at coarser vertical resolution resulting in measurement gap at reservoir scale. Crosswell seismic bridges this measurement gap and provides enhanced imaging of the interwell space at reservoir scale (Figure 1).Crosswell seismic acquires two basic pieces of information; first, the direct arrivals between source and receivers are used to create a 2-D profile of seismic velocity (velocity tomogram), and second, reflection information from horizons above and below the source and receiver positions to create a structural image between the wells. The combined velocity and reflection imaging provides detailed information about the structure of a given reservoir as well as rock properties. Additionally, mode converted (S) processing will provide additional insight into the reservoir definition.The case study discussed here is from Bunyu field in East Kalimantan in Indonesia. It is a very difficult seismic area with high surface attenuation due to varying surface topography, unconsolidated weathering layer and presence of near surface coal seams. The formation is dominantly discontinuous sand-shale formations with intercalations of coal seams. Seismic interpretation becomes increasingly difficult as the surface seismic is not of high quality. Structurally, the acquisition area encompasses several major faults that create sub horst-graben features as shown in Figure 2. The map is primarily derived from well log information, since surface seismic data is of poor quality. Crosswell seismic was acquired over eleven (11) profiles, overlain on the structure map (Figure 2). The results of the profiles to be presented in this paper are highlighted in Figure 2 (right).The interwell spacing of these profiles ranged from 686 m to 1758 m, very challenging distances for the attenuative geological conditions. The profiles were chosen so as to maximize the coverage over the Bunyu field to help in refining the seismic interpretation and potentially to reduce the uncertainty in infill drilling decisions and field optimization. The seismic sections generated clearly show remarkable improvement over the existing seismic despite high seismic attenuation observed in this area. METHODOLOGYCrosswell seismic is an emerging technology that provides high resolution imaging of the subsurface at the reservoir scale and is used for delineating complex structure. The technique employs tomographic surveying, whereby a transmitter and receiver are deployed downhole in separate wells. As a result of the inherent source-receiver geometry, interwell velocity SUMMARY Surface seismic is fundamental information for reservoir mapping and in-fill drilling decisions. A good seismic is critical to successful development of a field. However, at times, the surf...
INTRODUCTIONTraditionally, measurements in oil & gas industry have inverse relation between formation vertical resolution and spatial coverage. The logs provide hi-resolution information but close to the wellbore while surface based measurements such as seismic & gravity provide field wide spatial coverage at coarser vertical resolution resulting in measurement gap at reservoir scale. Crosswell seismic bridges this measurement gap and provides enhanced imaging of the interwell space at reservoir scale (Figure 1).Crosswell seismic acquires two basic pieces of information; first, the direct arrivals between source and receivers are used to create a 2-D profile of seismic velocity (velocity tomogram), and second, reflection information from horizons above and below the source and receiver positions to create a structural image between the wells. The combined velocity and reflection imaging provides detailed information about the structure of a given reservoir as well as rock properties. Additionally, mode converted (S) processing will provide additional insight into the reservoir definition.The case study discussed here is from Bunyu field in East Kalimantan in Indonesia. It is a very difficult seismic area with high surface attenuation due to varying surface topography, unconsolidated weathering layer and presence of near surface coal seams. The formation is dominantly discontinuous sand-shale formations with intercalations of coal seams. Seismic interpretation becomes increasingly difficult as the surface seismic is not of high quality. Structurally, the acquisition area encompasses several major faults that create sub horst-graben features as shown in Figure 2. The map is primarily derived from well log information, since surface seismic data is of poor quality. Crosswell seismic was acquired over eleven (11) profiles, overlain on the structure map (Figure 2). The results of the profiles to be presented in this paper are highlighted in Figure 2 (right).The interwell spacing of these profiles ranged from 686 m to 1758 m, very challenging distances for the attenuative geological conditions. The profiles were chosen so as to maximize the coverage over the Bunyu field to help in refining the seismic interpretation and potentially to reduce the uncertainty in infill drilling decisions and field optimization. The seismic sections generated clearly show remarkable improvement over the existing seismic despite high seismic attenuation observed in this area. METHODOLOGYCrosswell seismic is an emerging technology that provides high resolution imaging of the subsurface at the reservoir scale and is used for delineating complex structure. The technique employs tomographic surveying, whereby a transmitter and receiver are deployed downhole in separate wells. As a result of the inherent source-receiver geometry, interwell velocity SUMMARY Surface seismic is fundamental information for reservoir mapping and in-fill drilling decisions. A good seismic is critical to successful development of a field. However, at times, the surf...
Bunyu field in East Kalimantan, Indonesia is both a structural & stratigraphic play dominantly represented by discontinuous sand-shale formations. The field is on production since 1950 but production on a decline since 1976 reaching a minimum production of 1000 bopd in 2009. A surprise discovery well (X-18) in 2010 demonstrated significant future potential for this brownfield reservoir and hence a need for better understanding of reservoir. The existing seismic (2005) was of poor quality leading to uncertainty in reservoir mapping. Hence the objective was to provide a better sub-surface image to ultimately aid in defining new well locations. The use of crosswell seismic technology was chosen to minimize known attenuation effects produced by weathering layer, static corrections and the presence of shallow coal streaks in the area and provide hi-resolution data for successful infill drilling.Data was acquired over 11 crosswell profiles to cover key portions of the Bunyu field in 2011. Two wells constitute a crosswell profile providing imaging between the wells. The inter-well distances (between 1000-1758m) achieved a world's first for the largest well separation in a commercial environment as well as in high attenuation formations. The crosswell data provided far superior seismic imaging revealing sub-seismic faults, new stratigraphic features which were not evident before. The available surface seismic (2005) was a time migration imaging and was of poor quality. Re-processing of surface seismic was undertaken that provided a little better imaging. Later, crosswell data was used for spectral equalization of surface seismic for integration. An integrated study incorporating crosswell seismic, re-processed surface seismic and logs provided a new structure for Bunyu field. Crosswell seismic profiles in the northern most part of the project area revealed a new fault which was not evident on surface seismic. This fault was tracked on the surface seismic which revealed a new fault block. In July 2011, Pertamina drilled a dry well X-28 (400m NW from producer well X-18) when the integrated study was on-going. The performance of this dry well (X-28) & other wells in the vicinity was well explained by the presence of this new fault delineated by crosswell seismic results. The presence of new fault necessitated moving the earlier planned well location (X-30) so that it fell within the new fault block.In Aug 2012, Pertamina drilled the re-located well (X-30) in the new fault block. This well proved to be a success and confirmed the new interpretation guided by crosswell seismic. It shows hydrocarbon potential in four (4) layers. It produced 1655 bopd & 0.6 MMscfd of gas. The rest of the zones are still to be tested. The crosswell seismic thus reduced seismic uncertainty resulting in informed in-fill drilling. It has contributed significantly to millions of dollars of additional revenue and cost savings for Pertamina through production and avoiding drilling dry wells.
During the evolution of the petroleum industry, surface seismic imaging has played a critical role in reservoir characterization. In the early days, borehole seismic (BHS) was developed to complement surface seismic. However, in the last few decades, a wide range of BHS surveys has been introduced to cater to new and unique objectives over the oilfield lifecycle. In the exploration phase, vertical seismic profiling (VSP) provides critical time-depth information to bridge time indexed subsurface images to log/reservoir properties in depth. This information can be obtained using several methods like conventional wireline checkshot or zero-offset vertical seismic profiling (ZVSP), seismic while drilling (SWD) or distributed acoustic sensing (DAS) techniques. SWD is a relatively new technique to record real-time data using tool deployed in the bottomhole assembly without disturbing the drilling. It helps to improve decision making for safer drilling especially in new areas in a cost-effective manner. Recently, a breakthrough technology, distributed acoustic sensing (DAS), has been introduced, where data are recorded using a fiber-optic cable with lots of saving. ZVSP also provides several parameters like, attenuation coefficient (Q), multiples prediction, impedance, reflectivity etc., which helps with characterizing the subsurface and seismic reprocessing. In the appraisal phase, BHS applications vary from velocity model update, anisotropy estimation, well- tie to imaging VSPs. The three-component VSP data is best suited for imaging and amplitude variation with offset (AVO) due to several factors like less noise interference due to quiet downhole environment, higher frequency bandwidth, proximity to the reflector, etc. Different type of VSP surveys (offset, walkaway, walkaround etc.) were designed to fulfill objectives like imaging, AVO, Q, anisotropy, and fracture mapping. In the development phase, high-resolution images (3D VSP, walkaway, or crosswell) from BHS surveys can assist with optimizing the drilling of new wells and, hence reduce costs. it can help with landing point selection, horizontal section placement, and refining interpretation for reserve calculation. BHS offers a wide range of surveys to assist the oilfield lifecycle during the production phase. Microseismic monitoring is an industry-known service to optimize hydraulic fracturing and is the only technique that captures the induced seismicity generated by hydraulic fracturing and estimate the fracture geometry (height, width, and azimuth) and in real time. During enhanced oil recovery (EOR) projects, BHS can be useful to optimize the hydrocarbon drainage strategies by mapping the fluid movement (CO2, water, steam) using time-lapse surveys like walkaway, 3D VSP and/or crosswell. DAS has brought a new dimension to provide vital information on injection or production evaluation, leak detection, flow behind tubing, crossflow diagnosis, and cement evaluation during production phase. This paper highlights the usage of BHS over the lifecycle of the oilfield.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.