Publications

Quartz cementation is the most notable diagenetic signature in the Plover reservoir sandstone of the Abadi gas field. It occurs mostly as an overgrowth on the surfaces of detrital quartz grains to a variable degree over the field, and is suspected as a major cause for porosity and permeability reduction of the reservoir. An integrated image analysis was applied to the reservoir sandstones by utilizing cathodoluminescence microscopy, which allowed the volume of quartz cement as well as the depositional texture to be determined in a highly quantitative manner. The analysis has revealed that the amount of quartz cement has negative correlation with the mean grain size for the quartzose sandstones, indicating strong dependence on the depositional texture. The impact of the quartz cementation is interpreted to be quite significant especially on the permeability reduction probably because finer-grained texture provides not only initially-narrower pore throat size, but also more intensive quartz cements in the pore spaces. Structural restoration was also carried out, together with the regional petroleum system analysis, aiming to unravel the burial and the hydrocarbon filling history of the structure. The results indicate that prior to the formation of the current Abadi structure, the northern part of the field area was situated at a relatively shallower depth than the southern part for most of the Tertiary period, implying predominance of lower formation temperatures in the northern part. Because of this, possibly together with the earlier entrapment of the gaseous hydrocarbons in the northern part, the quartz cementation was retarded more effectively in the northern part than in the southern part of the field. The burial and thermal effect on the quartz cementation was also examined from the forward modeling approach, which also suggests that the northern part was at the relatively preferable condition for preservation of the reservoir quality. In summary, the present reservoir quality is concluded to be strongly constrained by the amount of quartz cement originated from the burial and thermal history as well as from the initial depositional texture. Although each of these factors affects the quartz cementation quite differently in areal and vertical scales from the other, both are considered to be of equal importance as controls on the reservoir quality.