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Summary Based on 3D high-resolution seismic data,and in the combined use of the logging,geologic,and drilling data,this paper provides a set of fluvial reservoir prediction methods used in Gangdong oilfield. It mainly includes: 1. Using the 3D seismic coherence technique to predict sedimentary sub-facies; 2. Using flatten slices technique to predict the spreading direction of the sandstones; 3. Using the horizon slice technique to determine the boundary of the sandstone; 4. Using 3D visualization technique to depict the sandstone configuration; 5. Using spectral decomposition to predict river channel structures. We have found a series of river channel sandstones based on our studies. The drilling result showed that our they were of great success,bringing significant geological achievements and considerable economic interests,and opening up a new exploration horizon for lithological prospect of the river channel sandstones in Dagang Oilfield. Introduction The main oil-bearing target layer in Gangdong oilfield lies in the lower part of Nm Formation,which is a typical secondary fluvial pool. The reservoir exists in the typical meander sedimentary sandstone and is mainly formed in fine sandstones and siltstone. The average porosity is over 32% and the permeability is 1002×10-3um2 in the sandstones mainly containing shale cementing. The structures are relatively simple; a few faults grow around the periphery of the oilfield,therefore the spread of the reservoirs obviously affect oil and gas accumulation. We studied the sedimentary environment of the area using fluvial sandstone reservoir prediction technique,confirmed the spread of favorable zones,found several sets of river channel sandstone, offered some rolling exploration objects, and finally obtained great geological achievements,so that we have the foundation in studying and finding stratigraphic reserveoirs in Gangdong oilfield. 1. The problem of prospect and exploit in Gangdong Oilfield Gangdong oilfield is located in the middle-eastern part of the Beidagang Structural Belt of Huanghua Depression and is connected with the oil-enriching Qikou Sag. It is the Neocene secondary pool controlled by the Gangdong Fault. During the past forty years’ exploration and production,the oil yield has become rather low. We have got to know that the quality of the seismic data collected here are too poor to accurately describe the reservoirs with sharp variation in both vertical and horizontal directions. It is difficult to identify the river channel sandstones; the stratigraphic zonation is inconsistent and there are a lot of contradicttions among different wells; some factors affect the complex reservoirs. The acquisition of the 3D high-resolution seismic data in Gangdong and the high-resolution processsing makes it possible to further conduct stratigraphic traps reservoir studies. 2. Main researching methods The research of characteristics of fluvial facies sandstones The characteristics of logging and coring By logging and coring,we can see that the sandstones of fluvial channels are mainly very fine with large sedimenttary beds. This is typically a meandering river deposition. The types of sandstones are of point bars and abandoned channels. Sandstones on the steep side are thicker and of a abrupt contact with mudstones; sandstones on the other side are thinner and interbedding with mudstones,which is the result of lateral migration of sandstonebars of the meandering river.
- Geophysics > Seismic Surveying > Seismic Interpretation (0.91)
- Geophysics > Seismic Surveying > Seismic Processing (0.71)
- Asia > China > Tianjin > Bohai Basin > Huanghua Basin > Dagang Field (0.99)
- Asia > China > Hebei > Gangdong Field (0.99)
Introduction Traditional models characterize the modern Mahakam Delta as a mixed river-dominated and tide-dominated delta that is presently prograding (e.g Galloway, 1975; Allen et al., 1976; Gastaldo et al., 1995; Allen and Chambers, 1998) and are commonly used as analogs to interpret subsurface successions. However, a recent quantitative study that describes the modern delta as transgressive and depositing a transgressive succession with very high preservation potential (Salahuddin and Lambiase, 2013) invalidates the use of the modern delta as a viable analog for progradational subsurface successions and suggests that transgressive successions may be relatively common in the subsurface. The Modern Mahakam Delta Quantitative hydrodynamic and sedimentologic data demonstrate the transgessive character of the modern delta that causes back-filling of the distributaries and relatively minor reworking of pre-transgression sediment. Very low wave energy in the receiving basin, plus rapid subsidence and burial, limits marine reworking to the uppermost pre-transgression strata and preserves the pre-transgression, progradational distributary and inter-distributary morphology. Ongoing back-filling of the distributaries is generating fining-upward successions that become increasingly marine upward. Current speed, and sediment transport capacity and competence decrease seaward so that the sediment flooring the distributaries is progressively finer downstream, which generates a fining-upward succession as transgression continues (Salahuddin and Lambiase, 2013). These successions also become more marine upward and have excellent preservation potential because of rapid subsidence rates and minor marine reworking. Sandy back-filled distributary successions are somewhat thinner and closer together in the upper delta plain than in the lower delta plain. As these sands fill the topographically low distributaries, they are laterally adjacent to slightly older, pre-transgression progradational strata. In contrast, inter-distributary areas are developing relatively thin, sandstones directly above pre-transgression progradational strata and separated from it by a transgressive erosional surface generated by marine reworking. The three dimensional geometry of the sandstones within a transgressive succession is expected to be complex and highly dependent on the pre-transgression delta morphology. The back-filled distributary sandstones are sinuous and oriented quasi-perpendicular to the shoreline while the transgressive shoreline sandstones are shoreline-parallel with a lateral extent that is determined by the distributary spacing. Ongoing transgressive lobe-switching means that the back-filled distributary successions are not exactly contemporaneous and that they probably have highly variable thicknesses and lateral extent.
- Geology > Sedimentary Geology > Depositional Environment (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Geological Subdiscipline > Stratigraphy (1.00)
Lithological Variability of Electrical Parameters in a Sandstone Sequence
Amabeoku, Maclean O. (Research Institute-King Fahd University of Petroleum and Minerals) | Mimoune, Kissami (Research Institute-King Fahd University of Petroleum and Minerals) | Al-Nufaili, Subhi (Research Institute-King Fahd University of Petroleum and Minerals)
Abstract Electrical parameters are the constants in the Archie equation and variants thereof, to calculate water saturation, original oil-in-place, and residual oil saturation from resistivity well logs. The applicability of these parameters in reservoir calculations are, in many cases, reservoir specific. It is, therefore, imperative that determinations of these parameters in the laboratory should be done at conditions that reflect, as closely as possible, those prevailing in the reservoir, with respect to temperature, pressure, and fluids. The formation factor, cementation exponent, and saturation index vary with lithology as well. The lithofacies identified in this sandstone sequence include clean sandstone, shaly sandstone, and sideritic sandstone. X-ray diffraction analysis shows the mineralogical composition to be clays, ankerite, siderite and quartz. An experimental program has been conducted to determine these electrical parameters at reservoir conditions using native crude oil on two of the lithofacies identified in the reservoir. This paper discusses results of these measurements. The results are grouped by lithology so that a regime of application can be defined. The importance of this lithological grouping is that different parameter values and lithology flags (or indicators) can be programmed into the water saturation calculation scheme to refine the well log determination of water saturation from Archie-type equations. P. 531
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Mineral > Silicate (1.00)
Abstract Predicting the nature and extent of deformation adjacent to wellbores can be critical for successful subsurface operations. The ability to capture the onset and evolution of failure can permit more efficient operations and circumvent or minimize the effects of well-known operational issues such as wellbore instability and sand production. In this paper, the behaviour of porous sandstones is investigated through replication of experimental testing conducted by Haimson (2004). In this work the deformation near the excavated section for highly porous sandstones was documented and analyzed, with contrasting deformational styles observed that are tentatively attributed to mineral composition. The requirements for predicting these styles are discussed and presented within a novel three-field modelling framework that incorporates a sophisticated constitutive model. Application of the workflow and results for breakout and sand control studies is discussed, along with potential future extensions to the capabilities of the constitutive model. Introduction Instability of subsurface excavations is critical and can pose serious problems affecting the timing and success of a project. Prediction of such instabilities has long been recognised as a key factor in many industries. Understanding the failure mechanisms is vital for the optimisation of well production as instabilities affect drilling efficiency, resulting in lost circulation, breakouts, or hole closure and even in loss of the open-hole section due to stuck and damaged drill pipe (Lang et al., 2011). Nevertheless, such instabilities are useful for informing on stress directions and magnitudes (Haimson and Song, 1993). Borehole logging has been long used to estimate stress directions, based on the location of the breakouts around the well (Brudy et al., 1997; Zoback et al, 2003; Kingdon et al., 2016). In addition, several studies have suggested that the characteristics and dimensions of the breakouts, if properly measured, can also inform on the magnitudes of far-field stresses.
- North America (0.30)
- Europe > United Kingdom (0.28)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.92)
ABSTRACT INTRODUCTION Biot's equations for wave propagation in poroelastic media [1-5] describe elastic and transport properties of fluid-saturated porous rocks. Skempton's pore pressure buildup coefficient [6] appears in the constitutive equations of Biot theory [7-10]. Thus this parameter is essential for many problems in reservoir engineering and exploration geophysics. We present laboratory measurements of Skempton's coefficient [6,9]. Since clays, microcracks, varying grain compositions and shapes, and porosity uncertainties complicate physical properties of rocks, we used synthetic sandstones made from sintered glass beads for most of our measurements. We also made measurements using a natural sandstone, and investigated the effects of clay and of undersaturation. BACKGROUND AND METHOD Skempton's coefficient B is defined as the change in pore-fluid pressure Pf with change in confining pressure Pc [6,9]. Related rock properties include porosity ø, dry-frame modulus K, unjacketed frame modulus Ks, and unjacketed pore compressibility 1/K ø, [7,11]. Using the generalized (lassmann's equation [7,8,11] that expresses the Blot coefficient relating fluid pressure to the increment of fluid content in a pore [4,5], we can write [Equation available in full paper] (1) and [Equation available in full paper] (2) where K! is the fluid bulk modulus and K, is the undrained bulk modulus [7]. Thus B can be estimated using measured values of moduli. B 1 for low porosity rocks as ø 0 in (1) and Ku -, Ks in (2). Also B 1 if K 0 as in soils, and B 1 if K ø Kf. Previous studies of B have generally compared observations to theoretical estimates calculated from literature values for the parameters K and Ks [e.g. 9,10], and usually K ø = Ks is assumed [8-12]. B has been measured at low differential pressures Pd -= Pc-Pf in fully saturated samples [9] and at high Pd in initially undersaturated samples [12], but both fully saturated and undersaturated conditions for the same sample have not been investigated. Here we calculate B using values of K, Ku, and Ks determined for our samples [13], and measure B for Pd ? 0.0-21 MPa. We made synthetic sandstones by sintering soda-lime glass beads with diameters of 230± 20 pm at peak temperatures of 720-760°C to achieve ø ranging from 0.15 to 0.39. Samples had lengths and diameters of ~5 cm. Kaolin was added into the pores of two samples. We also used a Massilion sandstone sample. Since we obtained similar results for all samples, here we only discuss one synthetic sandstone having ø = 0.393 ± 0.005. B measurements were made using the apparatus described by Green and Wang [9]. Our technique differed only in that filtered de-ionized water was used instead of kerosene for the pore fluid. Because our synthetic sandstones were extremely permeable we had >99% initial saturation. We measured Pf as Pc was increased from atmospheric pressure to 69 MPa, and then as Pc was again lowered. Measurement uncertainties for Pf and Pc were +1% for pressures of 4-69 MPa; measurements for lower pressures were less reliable.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)