Sains Malaysiana 46(11)(2017): 2163-2167

http://dx.doi.org/10.17576/jsm-2017-4611-17

 

The Application of Fractal Dimension on Capillary Pressure Curve to Evaluate the Tight Sandstone

(Aplikasi Dimensi Fraktal ke atas Lengkung Tekanan Kapilari untuk Menilai Batu Pasir Padat)

CHUNHUA GUO¹, YU YANG^2*, PING YAN², RUILI ZHOU³ & XIAODONG PENG⁴

 

¹College of Environment and Civil Engineering, Chengdu University of Technology, Chengdu 610059, China

 

²State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University

of Technology, Chengdu 610059, China

 

³Petro-Engineering Research Institute of North China Oil and Gas Branch, Sinopec, Zhengzhou 450006, China

 

⁴Research Institute of Zhanjiang Branch, CNOOC Energy Technology & Services Co. Zhanjiang 524057, China

 

Received: 6 January 2017/Accepted: 12 June 2017

 

ABSTRACT

The rock of gas tight reservoir is more heterogeneous than that of conventional sandstone reservoir and is more prone to water-blockage because of the invasion of operation fluid. This paper presented a new approach for the analysis of the capillary pressure curve for tight gas reservoir. Herein, the saturation equation with fractal dimension proved the previous observation that the log-log plot of capillary pressure against water saturation is a straight line, which is quite different from the popular observation by Corey’s correlation. How to transform the capillary pressure curve to relative permeability curve was also discussed with fractal dimension. The fractal dimension of capillary pressure, which is not only an indication of heterogeneity, can also reveal the potential water blocks in tight gas wells. If the rock has higher fractal dimension, being at the same water saturation, the capillary pressure will be higher and the relative permeability of water will be smaller, which means higher injection pressure is required to displace the trapped water in reservoir. It is suggested that for the tight gas pay zone with higher fractal dimension, more precautions should be taken to prevent the water trapping during drilling or stimulating operation.

 

Keyword: Capillary pressure curve; relative permeability; tight sandstone; water trapping

 

ABSTRAK

Batuan di takungan kedap gas lebih heterogen daripada takungan batu pasir konvensional dan lebih cenderung kepada penahanan air kerana pencerobohan daripada cecair operasi. Kertas ini mengemukakan pendekatan baru untuk analisis lengkung tekanan kapilari takungan kedap gas. Oleh itu persamaan penepuan dengan dimensi fraktal membuktikan pemerhatian yang lepas bahawa plot log-log tekanan kapilari terhadap air penepuan adalah garis lurus dan agak berbeza daripada pemerhatian popular oleh Pekali Corey. Bagaimana mengubah lengkung tekanan kapilari untuk ketelusan bandingan lengkung juga dibincangkan dengan dimensi fraktal. Dimensi fraktal tekanan kapilari bukan hanya sebagai petunjuk kontra, juga boleh mendedahkan potensi blok air dalam telaga gas yang padat. Jika batuan mempunyai dimensi fraktal yang tinggi pada penepuan air yang sama, tekanan kapilari akan menjadi tinggi dan ketertelapan relatif air akan menjadi kecil yang bermaksud tekanan pancutan yang tinggi diperlukan untuk menggantikan air yang terperangkap dalam takungan. Adalah disarankan agar zon kaksa kedap gas dengan dimensi fraktal yang lebih tinggi memerlukan lebih banyak langkah keselamatan untuk mencegah air daripada terperangkap semasa penggerudian atau operasi perangsang.

 

Kata kunci: Batu pasir padat; ketertelapan relatif; lengkung tekanan kapilari; perangkap air

 

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*Corresponding author; email: yangyu@cdut.cn