AVO analysis in high‐impedance sandstone reservoirs

Peddy, Carolyn P.; Sengupta, Mrinal K.; Fasnacht, Timothy

doi:10.1190/1.1437175

Cited by 6 publications

(1 citation statement)

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“…3 Seismic target processing technology for exploring SGR involves bright spot, AVO processing and G-log analysis skills etc. [4][5][6][7] Primary 2D and 3D seismic result data are processed to explore oil of mid-deep layers, so they can satisfy the need of structure interpretation. But when used to interpret bright spot, they obviously have 2 deficiencies 8 :…”

Section: Major Techniques Utilizedmentioning

confidence: 99%

A Successful Project of Progressive Exploration and Development for Shallow Gas Reservoir in Chenjiazhuang Arch

Sheng¹,

Cao²,

Xiang³

2001

All Days

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAimed at the characteristic that gas-bearing formation of shallow gas reservoir (SGR) shows bright spot on seismic cross-section, integrative technology research combining exploration and development has been developing in Shengli Oil Fields. After several years' practice, a series of techniques of progressive exploration and development with high benefit for SGR have been created. Studies and practice prove that bright spot on conventional seismic section has nature of multi-solution, i.e. some kinds of reservoirs, such as lithologic reservoir, hydrogenous sandstone, gas bearing hydrogenous sandstone and gas bearing sandstone, all show the characteristic of bright spot. In order to solve this problem, special purpose processing involving 3D, G-log and amplitude versus offset (AVO) is used to distinguish between real bright spots and false ones. Four gas-bearing regions including Yanjia, Chenjiazhuang, Gunan and Sanhecun have been discovered and put into production since 1988. 162 probable bright spots have been found, and 60 new wells drilled with 56 successful wells. Drilling success ratio advances from 55% to 93.3%. Incremental proven gas bearing area is 48.2 km 2 with gas initially in place 4.304×10 9 m 3 , and gas rate is 375× 10 3 m 3 /d. The spread application for this technology has been seeing considerable economic benefit, and it provides practical experience for exploiting such kind of reservoirs also.Progressive exploration and development utilizing technology of seismic bright spot accelerates the step of getting production. Four steps, including special purpose processing and seismic data interpretation, programming development plan and fulfilling drilling and gas lines construction, gaining gas productivity and submitting proven reserves, are all accomplished in the same year. This paper introduces a typical example for the course of progressive exploration and development in Chenjiazhuang Arch.

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Section: Major Techniques Utilizedmentioning

confidence: 99%

A Successful Project of Progressive Exploration and Development for Shallow Gas Reservoir in Chenjiazhuang Arch

Sheng¹,

Cao²,

Xiang³

2001

All Days

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Sensitivity of reflection seismic data to oil‐column height in high‐porosity sandstones

Ryan-Grigor¹,

Sayers²

2000

Geophysical Prospecting

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Tuning is the effect of interference between the reflections from the top and bottom of a thin layer on the amplitude of the composite reflection. For a homogeneous sandstone reservoir containing an oil column overlying brine, interference between the reflection from the top reservoir and the oil/water contact is a function of the height of the oil column. If the properties of the sandstone do not vary across the oil/water contact, the SS, PS and SP reflection coefficients from the oil/water contact are small in comparison to the PP reflection coefficient. This allows analytic expressions for the effective PP and PS reflection coefficients from the reservoir to be derived that include all P‐wave multiples within the oil column. For a given source/receiver offset, the component of the wavevector inside the oil column normal to the interface is larger for the PPPP reflection than for the PPPS reflection, due to the asymmetry in the raypath for the PPPS reflection. The PPPS reflection is therefore useful for determining oil‐column heights larger than that discriminated by the PPPP reflection, especially when used at wider offsets. A convenient classification of the AVO response of hydrocarbon‐bearing sandstone reservoirs overlain by shale is the scheme of Rutherford and Williams. Class 1 sands have higher acoustic impedance for normal incidence than the overlying shale, Class 2 sands have nearly the same acoustic impedance as the shale and Class 3 sands have lower acoustic impedance. Synthetic shot gathers calculated for these three classes as a function of oil‐column height show that a combination of the PPPP and the PPPS amplitudes can be plotted as a tuning trajectory, which can be used to determine the oil‐column height. This method is most sensitive for reservoirs that belong to AVO classes 1 and 2, and therefore may be useful in AVO analysis of Class 1 and 2 reservoirs where the traditional AVO indicators (developed for Class 3 reservoirs) do not work very well. These results demonstrate the usefulness of shear waves recorded in the marine environment at wide offsets.

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Rock‐physics forward modelling to predict seismic behaviour: A case study for exploration target in Mahanadi basin, East Coast of India

Mondal

Yadav

Chatterjee

2020

Geophysical Prospecting

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One of the major aspects of rock‐physics forward modelling is to predict seismic behaviour at an undrilled location using drilled well data. It is important to model the rock and fluid properties away from drilled wells to characterize the reservoir and investigate the root causes of different seismic responses. Using the forward modelling technique, it is possible to explain the amplitude responses of present seismic data in terms of probable rock and reservoir properties. In this context, rock‐physics modelling adds significant values in the prospect maturation process by reducing the risk of reservoir presence in exploration and appraisal phases. The synthetic amplitude variation with offset gathers from the forward model is compared with real seismic gathers to ensure the fidelity of the existing geological model. ‘Prospect A’ in the study area has been identified from seismic interpretation, which was deposited as slope fan sediments in Mahanadi basin, East Coast of India. The mapped prospect has shown class‐I amplitude variation with offset response in seismic without any direct hydrocarbon indicator support. The existing geological model suggests the presence of an excellent gas reservoir with proven charge access from the fetch area, moderate porosity and type of lithology within this fan prospect. But, whether the seismic response from this geological model will exhibit a class‐I amplitude variation with offset behaviour or ‘dim spot’ will be visible; the objective of the present study is to investigate these queries. A rock‐physics depth trend analysis has been done to envisage the possibilities of class‐I reservoir in ‘Prospect A’. Forward modelling, using a combination of mechanical and chemical compaction, shows the synthetic gas gathers at ‘Prospect A’, which are class I in nature. The study has also depicted 2D forward modelling using lithology and fluid properties of discovery well within similar stratigraphy to predict whether ‘dim spot’ will be seen in seismic. The estimated change in synthetic amplitude response has been observed as ∼5% at contact, which suggests that the changes will not be visible in seismic. The study connects the existing geological model with a top‐down seismic interpretation using rock‐physics forward modelling technique to mature a deep‐water exploratory prospect.

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AVO analysis in high‐impedance sandstone reservoirs

Cited by 6 publications

References 0 publications

A Successful Project of Progressive Exploration and Development for Shallow Gas Reservoir in Chenjiazhuang Arch

A Successful Project of Progressive Exploration and Development for Shallow Gas Reservoir in Chenjiazhuang Arch

Sensitivity of reflection seismic data to oil‐column height in high‐porosity sandstones

Rock‐physics forward modelling to predict seismic behaviour: A case study for exploration target in Mahanadi basin, East Coast of India

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