An application of seismic attributes analysis for mapping of gas bearing sand zones in the sawan gas field, Pakistan

Abstract

Sandstone intervals of the Lower Goru Formation of the Cretaceous age are proven reservoir intervals in the middle Indus Basin, Pakistan. However, based on seismic data interpretation, it is difficult to differentiate payable gas sand from non-payable gas sand. Various types of post-stacks seismic attributes are extracted and analyzed to differentiate payable gas sand from non-payable. The analysis reveals that average instantaneous frequency, peak spectral frequency, average instantaneous phase and sweetness seem to be more effective attributes along with energy half time. Sweetness attribute map shows two sweet spot below the targeted window which indicate to the presence of gas play. Statistical analysis is also carried out to find the associations between seismic attributes and thickness of gas layer values. Cross plots of these attributes were quantified through regression analysis. A good correlation with regression coefficient (R 2 ) [ 0.78 is found between seismic attributes and gas layer thickness except average instantaneous phase attribute, which lays the foundation for predicting the thickness of gas reservoir.

Sweetness analysis of Lower Goru sandstone intervals of the Cretaceous age, Sawan gas field, Pakistan

“…However, non-producing Gajwaro-01 well is located at the edge of low impedance zone as shown in Figure 15. The studies of Munir et al (2011) and Azeem et al (2015) also support our results. This sweetness zone covers an area of 49 km 2 and seems to be favorable for gas.…”

“…However, when the objective is to find the accurate location, size, vertical and horizontal extent of the sweet zones then quantitative interpretative methods need to be applied (Huang et al, 2009;Wagner et al, 2012). Different types of quantita-tive methods and techniques such as seismic attributes, amplitude versus offset (AVO) analysis, neural network and rock physics models are used to analyze the seismic amplitudes anomalies (Avseth et al, 2005;Chi and Han, 2009;He et al, 2011;Khalid et al, 2014;Azeem et al, 2015Azeem et al, , 2017. Mostly these techniques provide very accurate results on the basis of 3D seismic data analysis.…”

“…However, the logging and drilling results confirm that the sands of early Cretaceous age of Lower Goru formation are proven reservoir rocks in the middle and lower Indus basin (Ahmad et al, 2004). Ibrahim (2007) and Afzal et al (2009) studied the area based on amplitude anomalies however, their studies cover the eastern side of the study area whereas a significant potential is untapped towards the western side of the area (Munir et al, 2011;Azeem et al, 2015). Thus, available data sets have been integrated through constrained sparse spike inversion in order to accurately demarcate the sweetness zones in the B and C sands of this area.…”

Reservoir Characterization of the B-Interval of Lower Goru Formation, Miano 9 and 10, Miano area, Lower Indus Basin, Pakistan

“…The summation of results obtained by using Eqns. (6) to (14) for the Zone A of B-interval in Miano-9 and B-interval of Miano-10 are summarized in the Tables 4 and 5 respectively. Rock physics is the term that contains the techniques relating the geological properties of rocks with the corresponding elastic and seismic properties under certain physical conditions [19].…”

Porosity Distribution and Differentiation of Different Types of Fluids in Reservoir of Sawan Gas Field, Lower Indus Basin, Pakistan

“…The Indian Shield bounds the eastern side of the study area, whereas the Kirthar and Suleiman foldand-thrust belts mark its western boundary ( Figure 1) [3,11]. Regional geological data indicate that the structural evolution of the Sawan gas field was closely controlled by three post-rift tectonic events: (a) Late Cretaceous uplift and erosion, (b) NW-trending thick skinned wrench faulting, and (c) Late Tertiary to present-day tectonic uplift of the Jacobabad and Khairpur Highs [12]. These latter structural highs played an important role in the formation of structural and stratigraphic traps, not only in the Sawan area, but also in multiple oil and gas fields in the middle Indus basin.…”