Characteristics and origin of abnormally high porosity zones in buried Paleogene clastic reservoirs in the Shengtuo area, Dongying Sag, East China

Abstract

There are three abnormally high porosity zones developed in buried Paleogene nearshore subaqueous fan and sublacustrine fan clastic reservoirs at 2,800-3,200 m, 3,250-3,700 m and 3,900-4,400 m, respectively, within the Shengtuo area of the Dongying Sag. Here the porosity of reservoirs buried deeper than 4,000 m can still be greater than 20%. Investigation of these three abnormally high porosity (AHP) zones in the 3 rd to 4 th analysis, core physical property testing and other technical methods. The results show that, the AHP primary intergranular pores (more than 50% of the total porosity), while secondary pores and micropores in authigenic clays may develop in some reservoirs. AHP reservoirs in the AHP zone of 3,900-4,400 m are dominated by micropores in matrix, visible pores are mainly grain dissolution pores but with low absolute content (< 1%), so this zone belongs to the micropores primary AHP zone. The genesis of the three AHP zones was studied to distinguish between porosity enhancement and porosity preservation. Our research shows that, in deeply buried clastic reservoirs in the Shengtuo area, mineral dissolution occurred in a relatively closed diagenetic system with high temperature and high salinity. Reservoir rocks underwent extensive feldspar dissolution, while detrital carbonate grains and carbonate cements show dissolution enhanced porosity only a little due to the precipitation of almost isovolumetric dissolution products in the nearby primary intergranular pores in forms of authigenic clays and quartz cements. Net enhanced porosity originating from feldspar dissolution is generally less than 0.25%. Thus, the subsurface dissolution has little impact on the mid-deep buried high porosity reservoirs. Reservoirs in braided channels of middle fans in sublacustrine fans and reservoirs in the middle-front of fan bodies of nearshore overpressure and early hydrocarbon emplacement have effectively retarded compaction and carbonate are the main controlling factors in the development of AHP zones.unexpectedly high porosity and permeability at substantial burial depth. Studies on the origin and distribution of these high-quality abnormally high porosity (AHP) reservoirs are of great importance for oil-gas exploration and production. is statistically higher than the porosity values occurring in typical sandstone reservoirs of a given lithology (composition and texture), age and burial/temperature history. In sandstones containing abnormally high porosities, such porosities

The coupling of dynamics and permeability in the hydrocarbon accumulation period controls the oil-bearing potential of low permeability reservoirs: a case study of the low permeability turbidite reservoirs in the middle part of the third member of Shahejie Formation in Dongying Sag

“…It is a Mesozoic-Cenozoic half graben rift-downwarped basin with lacustrine facies directly deposited on Paleozoic bedrocks (Cao et al 2014;Wang et al 2014b). The Dongying Sag is bounded to the east by the Qingtuozi Salient, to the south by the Luxi Uplift and Guangrao Salient, to the west by the Linfanjia and Gaoqing salients, and to the north by the Chenjiazhuang-Binxian Salient.…”

“…6m, n, o). The large proportion of micropores results in much lower permeability of reservoirs than that of other reservoirs with the same porosity (Yuan et al 2013(Yuan et al , 2015Cao et al 2014). So middle and high porosity low permeability reservoirs are common.…”

Selective dissolution of eodiagenesis cements and its impact on the quality evolution of reservoirs in the Xing’anling Group, Suderte Oil Field, Hailar Basin, China

“…Authigenic minerals consist mainly of calcite, analcite, and kaolinite. On the whole, detrital grains Compaction is a major factor affecting porosity and permeability reduction during reservoir burial (Lu et al 2015;Zhang et al 2014;Zhu et al 2010;Xu et al 2008;Cao et al 2012Cao et al , 2014Pittman and Larese 1991;Xi et al 2015). …”

“…The selective dissolution phenomena of different minerals in sediments have garnered quite a bit of attention from geologists in recent years (Cao et al 2014;Macquaker et al 2014;Turchyn and Depaolo 2011;Yuan et al 2015a). Macquaker et al (2014) and Turchyn and Depaolo (2011), for example, reported similar phenomena in fine-grained sediments (Macquaker et al 2014;Turchyn and Depaolo 2011) and Yuan et al (2015a) investigated the selective dissolution between feldspars and calcite in buried sandstones.…”

Factors influencing physical property evolution in sandstone mechanical compaction: the evidence from diagenetic simulation experiments

“…It inhibits compaction and protects primary pores and is of great significance to the development of mid-deep high quality reservoirs (Hunt 1990;Ma et al 2011;Bloch et al 2002;Cao et al 2014). In this paper, undercompaction simulation experiments with pressure coefficients of 1.2 and 1.4 were conducted on sample VI from the Silver Beach of Qingdao, eastern China (the same parameters as sample I) and sample VII from the Yellow River Estuary of Dongying, eastern China (the same parameters as sample IV), respectively, under an overburden pressure larger than 34 MPa.…”