Direct Detection of Hydrocarbons in Indian Oil Fields by Using IPDS
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reservoirs and turned dry. Bantumilli field was DIRECT DETECTION OF initially conceived as a 80 Sq.kms structural HYDROCARBONS IN trap. The first well drilled on this structure resulted in a dry hole. The subsequent seismic INDIAN OIL maps, presented a picture of dissected fault FIELDS BY USING IPDS blocks with localized structural highs. The wells drilled on these highs, one after the other, TECHNOLOGY ended in drilling of 5 abandoned holes. It was concluded that the accumulation of hydrocarbons is not controlled by structure E.D. Rode *, M.K. Mukherjee ** , Amborish ** ** alone. The presence of suitable reservoir Bordoloi , Pydiraju Jinagam . controls the accumulation of oil in this field. IPDS was executed to identify the location of the oil containing areas. This survey, found out the presence of 5 petroleum prospects, varying in area from 8 Sq.kms. to 3 Sq.Kms, in the Abstract northern portion of the block. Incidentally, all these identified prospects correspond well with Infrasonic Passive Differential Spectroscopy is a the structural traps, mapped from the seismic technology for direct detection of data. Additionally, IPDS confirmed the hydrocarbons. It detects the spectral signatures presence of the faults, earlier identified from over hydrocarbon reservoirs and is the seismic data. These five prospects characterized by spectral peaks in the 1-8 Hz recognized from the IPDS survey represent the range. Hydrocarbon reservoir is a frequency most suitable locations that contain additional converter and deforms the frequency of the oil in Bantumilli field. natural earth noise. These deformed signals on spectroscopic analysis produce unique spectral signatures. These signatures are used as Direct * GeoDynamics India., ** H.R.D. Mumbai. Hydrocarbon Indicator. This technology has been test verified in series of oil Provinces around the world, in areas including currently producing, depleted, abandoned fields and Introduction virgin reservoirs. The omnipresent earth noise registers This method was used for delineation numerous continuous seismic signals which of the Sanganpur oil field, Cambay basin, Gujarat and for locating the additional oil are usually rather weak and often considered bearing areas in Bantumilli field, K-G basin, as useless background noise only. However, Andhra Pradesh. The entrapment condition of this “noise” carries useful information, oil accumulation in Sanganpur field is unknown. which is contained in its characteristics, The reservoirs are too thin to be identified such as the frequency spectrum, or statistical from the seismic. The structural disposition of properties or non-linear behavior. Moreover, the field is also uncertain and the entrapment is conceived to be a combination type. IPDS it may contain a spectral signature conclusively projected the extension of the characteristic of the media or environment, remaining oil in this field. Bantumilli field which it has passed through. Infrasonic contains oil, gas, and condensate in multiple Passive Differential Spectroscopy (IPDS) is reservoirs. These reservoirs are sporadic, thin, the detection of spectral signatures observed non persistent, discontinuous and cannot be deciphered from the seismic sections. The over hydrocarbon reservoir (hydrocarbon – petrophysical characters of the reservoirs vary water multi component system in porous conspicuously from one location to the other. media). It is characterized by spectral peaks The reservoir do not indicate any specific in the 1-8 Hz range, quasi continuous depositional model or trend. As a consequence, duration and a correlation time of several the drilled wells did not encounter suitable seconds. Hydrocarbon reservoir is a or gas areas, uneven flood fronts and areas frequency converter, and deforms the that are not effectively drained by the frequency of the natural earth noise. The existing wells. It avoids the risk of drilling deformation of the natural earth noise unsuccessful infill wells and avoids spectra is characteristic in the low frequency workover and redrill operation of old wells. range between 0.2 to 10Hz. These deformed signals on spectroscopic analysis produce IPDS technology is very effective in unique spectral signatures, which are used as the development of a oil/gas producing Direct Hydrocarbon Indicator ( Fig..1) This fields. It detects the moveable hydrocarbons, technology has been test verified in series of indicates the thickness of the oil/gas column oil provinces around the world, in areas at different locations, delineates the oil/gas including currently producing, depleted, bearing areas. It thus locates the optimal abandoned and virgin reservoirs. In all position of production wells, injection wells cases, this characteristic signal was absent and delineation wells. The existing oil/gas (or its amplitude, several orders of wells serve as calibration units. Correlation magnitude weaker) at the rim or outside of between thickness of pay horizons and IPDS the oil bearing areas. RHI (Reservoir Hydrocarbon Indicator) is usually better than 70%. In fill well location can be identified by interpolation of calibrated grid data. In abandoned and depleted fields, this technology can be utilized to know the present oil/gas content at different locations. IPDS measurements confirmed presence of adequate oil in some of the abandoned fields. The subsequent new wells drilled in such abandoned fields, renewed production, from the recently drilled wells. This method is particularly very useful at the commencement of new exploration ventures. Since this technology Fig 1: Spectral signature of subsurface is independent of geographic location, hydrocarbon reservoir lithology, depth or tectonic activity, it can work in any geological regime. The areas This noninvasive technology can be that conceal prospective sedimentary rocks utilized, as an oil field monitoring tool for below the basaltic flows, the areas intensely investigation of the extent of the remaining affected by severe tectonic activity, the hydrocarbons in producing fields. It screens logistically difficult areas or the oil producing areas, determines the environmentally restricted areas, can be current net pay thickness of hydrocarbon efficiently surveyed by this technology. It column at different wells and evaluates the does not use any artificial noise and status of the infill wells. The most measurements are easily done through light remarkable application in the field sensor and recorders. Since the source of the monitoring is the identification of present sound is from the bottom of the earth, there oil/ water contact (OWC) and gas/water is no absorptions , dispersion or refraction contact (GWC). It also identifies bypass oil from the subsurface layers or structural over these two fields. The fields are complexity. Before drilling an exploratory Sanganpur in Cambay Basin, Gujarat and wild cat well, IPDS can identify the Bantumilli in K.G. Basin, Andhra hydrocarbon potential of the prospect and Pradesh.(Fig..2) can avoid drilling a dry hole. For better understanding of a potential hydrocarbon pool, this technology has high flexibility, fast turnaround online data processing, high mobility due to moderate equipment and small crews, low cost and environment friendly. The in-house designed ultra sonic seismometers are the core of the signal acquisition devices and the key for the detection and monitoring of subterranean hydrocarbon reservoirs. The IPDS technology has been applied successfully in almost 100 survey campaigns in a variety of geological and Fig 2: Sedimentary basins of India environmental situations, in different parts of the world. Sanganpur oil field, Cambay Basin, Gujarat: Implementation of IPDS in Sanganpur oil field is situated in the Gujarat Indian oil fields state, in the northwestern region of India, in well explored, petroliferous Cambay The results of IPDS survey in the sedimentary basin. Cambay basin is an exploration, development and monitoring of intracratonic rift graben, between Saurashtra different oil/gas fields in different oil uplift and Aravalli ranges, extending in a provinces, established the success of this roughly N-S alignment, as a long and technology for direct detection of narrow depression from north Gujarat to hydrocarbon. This technology was Gulf of Cambay. The Sanganpur field is implemented in two oil and gas fields of situated in the Ahmedabad-Mehsana India. These fields are located in two tectonic block of Cambay basin. The different sedimentary basins of India, in sediments from Lower Eocene to Recent totally different geographical location, represent the stratigraphy of the field. The subsurface configuration, lithological structural configuration of Sangapur field is sequence, tectonic regimes, depths and not conclusive from the seismic maps. The structural orientation. Both the fields have Time contour map of a reflector with in adequate seismic coverage, drilled wells and Mehsana Member, shows that this area producible reserves. Yet it is difficult to constitutes a gentle flank, deepening towards ascertain the actual hydrocarbon potential of south (Fig..3). However, a Isochron map, both fields and initiate production. In order corresponding to the bottom of Viraj shale to establish the petroleum potential of these formation indicates that a narrow fields in minimum time, IPDS was executed longitudinal anticline, having a gentle 10 m.sec. amplitude, represents the Sanganpur clean sand of 5m.thickness having good structure(Fig..4) . The two wells, viz. S-1 in petrophysical