Wyniki wyszukiwania - BazTech

1

Rock physics-based analysis to discriminate lithology and pore fluid saturation of carbonate reservoirs: a case study

Makarian Esmael, Elyasi Ayub, Moghadam Rasoul Hamidzadeh, Khoramian Reza, Namazifard Pedram

Acta Geophysica

|

2023

|

Vol. 71, no. 5

2163--2180

EN

Rock physics templates (RPT) and modeling contribute significantly to accurately and fast characterization of hydrocarbon reservoirs. This study strives to characterize lithology and pore fluid saturation for a carbonate reservoir in southwest Iran using RPT by well-logging data in a zone with a thickness of almost 100 m. To discriminate lithology, Greenberg–Castagna and Gardner models were applied. Also, velocity ratio - Gamma-ray (GR) and density - GR templates were implemented to investigate more. Results show that the researched zone’s lithology consists of a considerable amount of limestone, followed by dolomite, and a small amount of shale, without sandstone, which matches excellently with the lithology column and geophysical logs. For fluid discrimination, two different rock physical directions were impalement. Firstly, the rock physics model of the study area was built through Xu and Payne’s model. Then, velocity ratio - acoustic impedance template (Vsub>p/Vsub>s–AI) was applied to modeled data scaled with resistivity and porosity and then successfully validated with oil and water saturation. Findings show that PRT organizes data concerning similar features (here, aspect ratio), causing easy, fast, and more accurate analysis, and fluid content in the study includes oil and water, which the figure for oil is much more. In different oil and water saturation, non-modeled data were investigated through Vsub>p/Vsub>s − Vsub>s, Vsub>s − Vsub>p, and shear impudence (SI) - AI template supported by pore-pressure (PP) information to further research fluid distribution and its effect in the second direction. Regarding the rock physical analysis, the main reason for the decrease in seismic velocities and impedances is high pore pressure due to high oil saturation.

2

Experimental study of relationship among acoustic wave, resistivity and fluid saturation in coalbed methane reservoi

Xiao Kun, Duan Zhongyi, Yang Yaxin, Li Hongxing, Qin Zhen, Luo Qibin

Acta Geophysica

|

2023

|

Vol. 71, no. 3

1241--1249

EN

Experimental study of logging petrophysical parameters is very important for the establishment of logging evaluation model of coalbed methane reservoir. The acoustic and resistivity measurements of coal rock samples taken from the southern Qinshui Basin in China were measured under dry and saturated conditions of different salinity solutions. The variation laws of acoustic velocity and waveform with saturated salinity were analyzed. The changes of resistivity with temperature and pressure conditions were also analyzed. With the increase in salinity, acoustic velocity showed parabolic attenuation characteristics. The fluid content of coal samples can be judged by the acoustic wave. The waveform of dry coal sample presented multiple excitation state, and the waveform had larger fluctuation and smaller amplitude. The waveform of saturated salinity coal sample presented stable and smooth fluctuation characteristics. The resistivity of coal rock decreased exponentially with the increase in pressure. The property of fluid in pores can be judged by the sensitivity of resistivity of coal rock to temperature.

3

The variation of free gas distribution within the seeping seafloor hydrate stability zone and its link to hydrate formations in the Qiongdongnan Basin

Wei Deng, Jinqiang Liang, Zenggui Kuang, Tong Zhong, Yanian Zhang, Yulin He

Acta Geophysica

|

2022

|

Vol. 70, no 3

1115--1136

EN

China geological survey has conducted two hydrate expeditions for two gas chimney structures (GC1, GC2) in the Qiongdongnan Basin, South China Sea, where the fluid migrations vary significantly. Although massive hydrates were recovered both in the seepage pathways above GC1 and GC2, the free gas distributions in seeping seafloor hydrate stability zone (HSZ) remain controversial. Previous studies confirm that structure I (sI) and structure II (sII) hydrates occur through the whole seepage pathways, and free gas accumulates below the base of methane hydrate stability zone (BHSZ). In fact, free gas and gas hydrates coexist in the whole seepage-gas chimney system. The quantitative estimation of the fluid distribution is significant for studying the heterogeneous fluid migration in the seepages. In this study, Archie formula and three-phase Biot-type equation are modified to invert fluid concentrations for the whole well sections, in which brine, free gas, gas hydrate and matrix are considered as separate phases. The results indicate that the bottom simulating reflector is the boundary of an increasing gas concentration and a decrease hydrate concentration, instead of the interfaces of the hydrate and free gas in most areas. And hydrate occurrence is closely related to the micro-fault in the gas chimney. By comparing the fluid distribution between GC1 and GC2, more free gas associated with gas hydrates is accumulated in the seepage pathways in HSZ in GC1 where less free gas occurred below the BHSZ. Gas-bearing fluids in GC1 are considered to be very active in historic time, but they nearly stop flowing now, and the remaining gas cannot form hydrates in the hydrate-saturated pores, while the fluids in GC2 tend to convert to hydrates till now, and it is an active or younger fluid system. Free gas is the important intermediate medium for revealing this phase transition and exerts a significant control on the timescales associated with phase equilibrium variation processes. It is the first study revealing the relationship between the fluid distribution and the mobility of the seepage-gas chimney system in the study area, which also provide a new insight for estimating hydrate resource.

4

Rock physics based estimation of quartz content in the Shenhu area, South China Sea

Deng Wei, Liang Jinqiang, He Yulin, Kuang Zenggui, Meng Miaomiao

Acta Geophysica

|

2020

|

Vol. 68, no. 6

1619--1641

EN

Estimation of quartz content (QC) is important for gas hydrate production. However, the existing methods pay more attention to estimate saturations of hydrate or free gas instead of QC. QC is difcult to be estimated because of its limited and unclear infuences on velocities in the hydrate-bearing sediments. A workfow was proposed to estimate QC from core to logging to seismic inversion whose core technologies were an unconsolidated anisotropic model (UAM) and an inverse modeling approach. We used the UAM to construct the quantitative relationships between physical properties including QC and velocity. Then, the velocities of the reservoirs were obtained by logging-constrained seismic inversion. Finally, QC can be scaled by the inverse modeling of the UAM. To build the UAM, we analyzed the physical properties of hydrate reservoirs based on the cores and logging while drilling (LWD) data in the Shenhu area, South China Sea, and characterized unconsolidated sediments with horizontally layered hydrates and gas occurrences. The calculated P-velocities and S-velocities from the UAM agreed with the LWD data when the input variables were QC, porosity, hydrate saturation, and gas saturation. Conversely, for a group of P-velocity and S-velocity from seismic inversion, the corresponding QC can be scaled out as well as the other parameters based on the UAM, which was defned as an inverse modeling. Because the signifcant parameters such as hydrate saturation have been considered as independent variables in the model, we can efectively avoid the correlation between QC and the others. Prediction multiplicity can be reduced. The estimated QC was consistent with the drilling and geological understanding in the feld application, indicating that the method proposed is efective and practical.

5

Effect of Shale Distribution on Hydrocarbon Sands Integrated with Anisotropic Rock Physics for AVA Modelling: A Case Study

Ali A., Zubair, Hussain M., Rehman K., Toqeer M.

Acta Geophysica

|

2016

|

Vol. 64, no. 4

1139--1163

EN

Shales can be distributed in sand through four different ways; laminated, structural, dispersed and any combination of these aforementioned styles. A careful analysis of well log data is required for the determination of shale distribution in sand affecting its reservoir quality. The objective of this study is to characterize the effect of shale distribution on reservoir quality of sands using well log data. The correlation of well data in terms of lithology has revealed four sand and three shale layers in Lower Goru Formation acting as a major reservoir in the study area. Our results indicate that the laminated type of shale distribution prevails at the Basal sand level, which does not affect its reservoir quality greatly. The remaining layers of variable vertical extent show a variety of shale distribution models affecting their reservoir quality adversely. We also present anisotropic rock physics modelling for AVA analysis at Basal sand level.

6

An Estimation Method of Pore Structure and Mineral Moduli Based on Kuster–Toksöz (KT) Model and Biot’s Coefficient

Peng D., Yin C., Zhao H., Liu W.

Acta Geophysica

|

2016

|

Vol. 64, no. 6

2337--2355

EN

Pore structure and mineral matrix elastic moduli are indispensable in rock physics models. We propose an estimation method of pore structure and mineral moduli based on Kuster-Toksöz model and Biot’s coefficient. In this technique, pore aspect ratios of five different scales from 100 to 10-4 are considered, Biot’s coefficient is used to determine bounds of mineral moduli, and an estimation procedure combined with simulated annealing (SA) algorithm to handle real logs or laboratory measurements is developed. The proposed method is applied to parameter estimations on 28 sandstone samples, the properties of which have been measured in lab. The water saturated data are used for estimating pore structure and mineral moduli, and the oil saturated data are used for testing these estimated parameters through fluid substitution in Kuster–Toksöz model. We then compare fluid substitution results with lab measurements and find that relative errors of P-wave and S-wave velocities are all less than 5%, which indicates that the estimation results are accurate.

7

NMR Parameters Determination through ACE Committee Machine with Genetic Implanted Fuzzy Logic and Genetic Implanted Neural Network

Asoodeh M., Bagheripour P, Gholami A.

Acta Geophysica

|

2015

|

Vol. 63, no. 3

735--760

EN

Free fluid porosity and rock permeability, undoubtedly the most critical parameters of hydrocarbon reservoir, could be obtained by processing of nuclear magnetic resonance (NMR) log. Despite conventional well logs (CWLs), NMR logging is very expensive and time-consuming. Therefore, idea of synthesizing NMR log from CWLs would be of a great appeal among reservoir engineers. For this purpose, three optimization strategies are followed. Firstly, artificial neural network (ANN) is optimized by virtue of hybrid genetic algorithm-pattern search (GA-PS) technique, then fuzzy logic (FL) is optimized by means of GA-PS, and eventually an alternative condition expectation (ACE) model is constructed using the concept of committee machine to combine outputs of optimized and non-optimized FL and ANN models. Results indicated that optimization of traditional ANN and FL model using GA-PS technique significantly enhances their performances. Furthermore, the ACE committee of aforementioned models produces more accurate and reliable results compared with a singular model performing alone.