Application of elemental capture spectroscopy in deep tight reservoir evaluation: A case study of well SK-2

doi:10.13745/j.esf.sf.2021.1.60

Abstract

Abstract:

There are multiple gas logging anomalies in the Shahezi Formation, Songliao Basin, indicating its tight gas potential. However, deep tight reservoirs in the area have strong heterogeneity, thin thickness, interlayer development and various types. Based on the analysis of conventional well log of well SK-2, we used elemental capture spectroscopy (ECS) well logging to finely retrieve the mineral component content for accurate lithology identification, and subsequently identified five types of reservoirs by crossplot analysis. Combined with petrophysical experimental data, we further obtained the reservoir evaluation parameters such as variable skeleton porosity, brittleness index, and organic carbon content, which allowed us to categorize the reservoirs into three groups based on the well logging data and comprehensive evaluation indexes. In the Shahezi Formation (3730-4500 m), the porosity values range between 5%-9%, and the brittleness indexes range between 45%-60%. TOC of adjacent source rock is generally high, with relatively large accumulative thickness, and depth intervals at 3798-3831, 3950-3990 and 4150-4200 m show favorable tight gas potential for exploration and development. We demonstrated in this paper that, ECS well logging can accurately evaluate tight gas reservoirs so as to provide a reference basis for fracturing optimization in tight reservoirs.

Key words: Songliao Basin, Shahezi Formation, elemental capture spectroscopy, tight gas, reservoir evaluation

CLC Number:

HAN Shuangbiao, TANG Zhiyuan, BAI Songtao, WAN Lei, RUI Yurun, GAO Yuan, HUANG Yongjian, WANG Chengshan. Application of elemental capture spectroscopy in deep tight reservoir evaluation: A case study of well SK-2[J]. Earth Science Frontiers, 2022, 29(1): 449-458.

Figures/Tables 10

Fig.1 Simplified regional geological map, geological cross-section of the Songliao Basin, and composite well log for well SK-2 showing the lithology profile. Modified from [11].

Fig.2 Elemental capture spectroscopy sonde

Fig.3 Core samples of the Shahezi Formation in well SK-2

Fig. 4 ECS well logging evaluation of elemental and mineral compositions of typical lithostrategraphic unit of the Shahezi Formation in well SK-2

Table 1 Typical characteristic logging response and mineral compositions of the Shahezi Formation in well SK-2

类型	岩性	测井曲线响应特征												矿物组分含量/%
		常规测井	元素测井											石英		长石		碳酸盐岩		黄铁矿		黏土
		自然伽马/API		w(Fe)/%		w(Ti)/%		w(K)/%	w(Si)/%		w(Al)/%			石英		长石		碳酸盐岩		黄铁矿		黏土
I类	粉砂岩	93			4.37		0.25			1.47		28.8	7.41		23		31		14.7		1.15		43	泥质粉砂岩、粉砂岩
II类	细砂岩	72.55			2.84		0.2			1.2		29.2	7.2		28		38		16.2		0.9		22	泥质细砂岩、细砂岩
III类	中砂岩	71.9			3.32		0.22			0.99		30.26	5.8		30		36		14.1		1		21.4	泥质中砂岩、中砂岩
IV类	粗砂岩	66.23			3.26		0.2			1.06		30.59	5.6		33		35		12.1		1.4		21	泥质粗砂岩、粗砂岩
V类	砂砾岩	69.2			2.95		0.18			1.13		32.8	5.17		51		33		8.6		0.88		11	砂砾岩、砾岩

Fig.5 Lithological classification crossplots for the Shahezi Formation in well SK-2

Fig.6 Comparison of calculated porosities by fixed and variable framework methods, grain size profile, and lithology profiles according to well log and ECS well logging for the Shahezi Formation in well SK-2

Fig.7 Comparison between brittleness/TOC profile by ECS interpretation and well log for the Shahezi Formation in well SK-2

Table 2 Comprehensive classification criteria for favorable intervals in the tight reservoirs of the Shahezi Formation in well SK-2

类别	主要岩性	$临近烃源岩总有机碳含量 / %$	孔隙度/%	脆性指数/%
一类	以砂砾、粗砂岩为主	≥1.7	≥5.4	≥44
二类	以中砂岩为主	1.4~<1.7	3.4~<5.4	40~<44
三类	以细、粉砂岩为主	<1.4	<3.4	30~<40

Table 2 Comprehensive classification criteria for favorable intervals in the tight reservoirs of the Shahezi Formation in well SK-2

类别	主要岩性	$临近烃源岩总有机碳含量 / %$	孔隙度/%	脆性指数/%
一类	以砂砾、粗砂岩为主	≥1.7	≥5.4	≥44
二类	以中砂岩为主	1.4~<1.7	3.4~<5.4	40~<44
三类	以细、粉砂岩为主	<1.4	<3.4	30~<40

Fig.8 Comprehensive evaluation of favorable reservoir intervals of the Shahezi Formation in well SK-2

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