Macrolithotype characteristics of coal seam and their controls on coalbed methane well productivity in the Hancheng block of the southeastern margin of Ordos Basin

ABSTRACT

Previous studies about factors on coalbed methane production cannot meet the need for refined development. This work attempts to study the impact of macrolithotype characteristics known before fracturing on well production, to enable the developer to predict the production potential of each well in advance and adopt a precise development strategy. Logging data of 216 wells were obtained to predict macrolithotypes distribution of No. 3, 5, and 11 seams in the Hancheng block. And macrolithotype characteristics were described from two aspects: the proportion of bright layers in thickness (PBLT) and the number of layers per meter (NLPM), and their impact on well productivity were evaluated respectively by analyzing the production data. The results show that PBLT value increases from No.11 to 3 seams. PBLT has a positive correlation with well productivity. Bright type has the highest productivity potential (771 m³/d), followed by semi-bright type (681 m³/d), and semi-dull type (436 m³/d). There is a negative correlation between NLPM and productivity. Stable type has the highest productivity potential (1049 m³/d), followed by relatively stable type (719 m³/d), and unstable type (405 m³/d). Thick coal seams with high NLPM may not have much production potential. Under multi-seam production, seams with high PBLT should be selected, and NLPM can be used as a critical index to estimate the inter-seam interference before fracturing.

KEYWORDS:

• Coalbed methane
• macrolithotypes characteristics
• well logging data
• well productivity
• multi-seam commingled production

Nomenclature

PBLT	=	Proportion of bright layers in thickness
NLPM	=	Number of layers per meter
PBLT type	=	Type of coal seam in terms of PBLT
NLPM type	=	Type of coal seam in terms of NLPM
$H_b$	=	Total thickness of bright and semi-bright layers in coal seams
$H$	=	Coal seams thickness
$N$	=	Number of macrolithotypes layers of coal seams
$H_b^i$	=	Thickness of bright and semi-bright layers in No. i seam
$H^i$	=	Thickness of No. i coal seam
$N^i$	=	Number of macrolithotype layers of No. i coal seam

Additional information

Funding

This work was financially supported by the Key Project of the National Science & Technology, China [Grant No. 2016ZX05042-002], the National Natural Science Foundation Project, China [Grant No. U1703126] and the Fundamental Research Funds for the Central Universities, China.