Song, Liang (Sinopec Shengli Oilfield Company) | Zhang, Yunyin (Sinopec Shengli Oilfield Company) | Zhang, Yingge (Sinopec Shengli Oilfield Company) | Tan, Mingyou (Sinopec Shengli Oilfield Company) | Sui, Zhiqiang (Sinopec Shengli Oilfield Company) | Gao, Qiuju (Sinopec Shengli Oilfield Company) | Zhang, Xiujuan (Sinopec Shengli Oilfield Company) | Liu, Jianwei (Sinopec Shengli Oilfield Company)
Shale oil reserves are of rich resources and great potential for exploration. Predicting shale brittleness comprehensively and accurately is of great significance to exploration and development of shale oil. Continental shale is characterized in that lateral lithofacies change fast, brittle mineral component changes considerably and much difference exists in buried depth. Past evaluation methods for brittleness based on elastic mechanical parameters or brittle mineral component, cannot accurately describe continental shale brittleness. This study proposes a prediction method of continental shale brittleness. Based on determination of the brittle-ductile transition depth in shale, combined with various pre stack and post stack seismic prediction technologies, it discusses the way to make seismic prediction of shale brittleness with different types of lithofacies and brittle mineral component. This method gets a preferable result in the prediction of shale brittleness in lower part of member 3 of Shahejie Formation (Es3) of LJ area in JY depression, eastern China, and it can provide some references for future exploration and development of continental shale oil.
In recent years, encouraged by successful experience in the North American, Chinese shale oil exploration is becoming a priority project. At present, shale oil has been found in Bohai Bay Basin, Chaidamu Basin and Biyang sag and other regions of China, and has become an important field of oil and gas exploration in high mature exploration area. In the exploration and development of shale oil, formation brittleness is the main index for evaluating shale oil, and is also the important reference to fracturing layer selection. Predicting shale brittleness comprehensively and accurately is of great significance to exploration and development of shale oil.
Continental shale is characterized by fast lateral lithofacies change, considerable brittle mineral component change and much difference in buried depth. There are two evaluation methods for brittleness at present, one is based on elastic parameters (Poisson's ratio, Young's modulus) without considering the effect of different types of lithofacies. Another is based on brittle mineral component (the content of carbonate, quartz feldspar content) without considering the effect of different types of lithofacies and changes of buried depth. These two methods cannot comprehensively and accurately describe continental shale brittleness. At present, rock mechanics experiment in shale core sample can determine the brittle-ductile transition parameters, which can be used to evaluate shale brittleness. But this method is limited to the calculation of core samples, which cannot be popularized.
The 1'st members of Yingcheng formation, lower Cretaceous in Xingcheng development area, Songliao Basin mainly have rhyolite gas reservoirs. The 1'st member of Yingcheng is belong to the low-porosity and low-permeable reservoir, the reservoir space are mainly fracture-pore. By the means of field out crops observation, core description, thin section analysis, well logging identification and the seismic forecasting, the fractures of 1'st member of Yingcheng volcanic reservoir was analyzed in three aspects: the genetic, the attitude and the width. The dominate fracture type of 1'st member of Yingcheng are the tectonic related fractures(78.5%), then the diagenetic related fractures(17.0%), corroded fractures(4.2%) are the last. The high angle fractures and the vertical fractures are most common in tectonic related fractures; the oblique fractures are the following. The dominate type of diagenetic related fractures are level fractures, followed by high angle and oblique fractures. The fractures in the reservoir were mainly wide fractures (width>1mm) and narrow fractures (0.1mm<width<1mm), the fractures of middle width are the minority. The distributions of the fractures were mainly controlled both by the regional stress field and the activity of the faults, the fractures are displayed by belts in coincident with the strike of the main faults.
Keywords: volcanic gas reservoir, reservoir fracture, structural fractures, diagenetic fractures, high angle fracture
The development and exploration of volcanic gas reservoir is now the hot spot in petroleum fields. The volcanic gas reservoirs have been discovered in Songliao basin, Chaidamu basin, Sichuan basin and so on[1-2]. It is quite difficult to study the fracture characteristics of volcanic gas reservoir. This paper takes the volcanic gas reservoir of the Yingcheng Formation of Xushen area in Daqing oilfield for example to study the fracture of volcanic reservoir.
The volcanic gas reservoir of the Yingcheng Formation in Xingcheng area is located in Shengping-Xingcheng structural belt of Xujiaweizi Fault-Depression in the north of Songliao basin, mainly developed in the first member of Yingcheng Formation in Lower Cretaceous Series. The buried depth of reservoir is 3000~3500m. The volcanic gas reservoir is mainly the rhyolite. The types of reservoir are mainly fracture-porosity style, which belongs to low porosity and low permeability reservoir.
1. Lithology and lithofacies characteristics
The lithology and lithofacies characteristics control the development of fractures and cavity, which is the dominant factor to make the types of reservoir space and reservoir heterogeneity complicate[3-4]. By the chemical analysis of core gathered from 7 wells, the chemical composition of volcanics is mainly the SiO2(74.24% on average) and next is Al2O3(10.4% on average) and K2O+Na2O(8.42% on average). The figure of alkaloid-SiO2 is made by the analysis ,which suggests that the lithology in the area is mainly acidic volcanic rock and the next is the intermediate lava. The type of rocks is mainly the rhyolite and others are the mixpah, trachydacite, dacite, andesite and necrolite.
Li, Hongbing (China University of Mining & Technology and Petrochina Company Limited) | Zhao, Wenzhi (Petrochina Company Limited) | Cao, Hong (Petrochina Company Limited) | Yao, Fengchang (Petrochina Company Limited)
This paper derives a scalogram formula of seismic wave in wavelet domain from the wavelet theory and the propagating equation of seismic wave in an anelastic medium. From the scalogram formula we present a method for estimating seismic attenuation based on scale shift data and define the centroid of scale for characterizing attenuation. In the absorbing medium, seismic attenuation decreases with scale in the wavelet domain, the small-scale energies of the seismic signal are attenuated more rapidly than the large-scale energies as waves propagate. As a result, both the peak scale and the centroid of the signal''s scalogram experience a upshift during propagation. Under the assumption of a frequency-independent
We report a new model relating porosity and formation resistivity factor. This model not only explains both Archie and non-Archie behaviors with non-conductive minerals, but also complies with meaningful physical bounds. We define an equivalent rock element aligned with the direction of measurement, in which the pore structure is comprised of two orthogonal components. One is oriented along electrical potential gradient and contributes most efficiently to current flow. The other is perpendicular to the gradient and contributes least efficiently per unit pore volume. The ratio of the former over the latter is defined as "pore structure efficiency". By adjusting pore structure efficiency, any rock can be equivalently represented. Formation resistivity factor can then be expressed as a function of total porosity and pore structure efficiency. Upon analyzing relevant factors in reservoir rocks, we approximate pore structure efficiency as a simple linear or power function of porosity. This leads to a new theoretical relationship between formation resistivity factor and porosity that:
explains and agrees with Archie's generalized first equation for a geologically realistic porosity range from 0 to 40%,
explains non-Archie phenomena, e.g. noticeable curvature in dual logrithm coordinate space of formation factor versus porosity,
is consistent with physical bounds from 0 to 100% porosity, e.g., the magnitude of slope is never smaller than 1, and tends to be 1 as porosity approaches 100%,
generalizes multiple porosity domain system into one transitionally smooth description,
contains a term representing pore structure efficiency independent of porosity that can be potentially used for fracture analysis,
is applicable to both isotropic and anisotropic media by definition.
Shallow gas reservoirs are widely distributed in China and mostly occur at depths shallower than 1500 metres (4921.50 ft). These occur as lenticular and marginal reservoirs, with small and scattered reserves, with quite complex gas-water relationship and edge/bottom water in the majority of sand-bodies. Each sand-body forms an unattached and closed gas-water system, but there is limited elastic energy in the aquifer. The production performance of one of such reservoirs is as follows:
Per-well initial gas rate is rather low with fast decline.
The reservoir has a gas drive to weak elastic water-drive.
Water incursion has obvious influences on production results.
Wellhead pressurse could be used to represent the changes of formation energy, for it is impacted little by wellbore accumulated liquid.
Finally, formation damage resulting from drilling, perforating etc. has noticble influences on the gas wells' performance.
Thus the main factors that could decide reasonable well rates should be the following factors: Efficient utilization of formation energy, reservoir structure should not be destroyed, accumulated liquids in the wellbore should be continuously removed. In addition better development results can be achieved through initial sand control and edge/bottom water fingering/coning should be minimised.
The purpose of this paper is to have a review of the parameters and the performance of the Shengli oil reservoirs. It could be used for reference for similar type of reservoirs.