Abstract
The Chang 7 oil group in the Ordos Basin has the characteristics of a tight lithology, a low formation pressure coefficient and strong reservoir heterogeneity. To better determine reasonable developmental technical countermeasures, oiliness, seepage capacity, and compressibility evaluations are combined. Using a combination of field practice and laboratory experiments, six types of sweetness classification evaluation parameters are screened: oil saturation, longitudinal oil layer structure coefficient, average pore throat radius, gas-oil ratio, brittleness index, and minimum horizontal principal stress. By combining the relationships among variables with the initial production from directional wells, the gray correlation method is used to quantify the weights of the contributions of evaluation parameters to production. On this basis, using the difference method for the curve slope, a sweetness evaluation and classification method for the Chang 7 oil group is constructed, and it solves the difficult problem of quality difference classification for the Chang 7 oil group and provides a reference basis for the optimal design of well patterns and fracturing reconstruction parameters.
Highlights
According to estimates by the U.S Energy Information Administration (EIA), China’s technically recoverable tight oil resources amount to 44.8 × 1 08 t, ranking third in the world (Zou 2011)
In the formula, LSE is the longitudinal structural coefficient of the oil layer; oh is the thickness of a single oil layer, m; n0 is the number of oil layers, piece; sh is the thickness of the sandstone, in m; and fh is the thickness of the formation, m
Ai(k) is the i-th evaluation parameter of the k-th well, and the unit is the corresponding unit of each parameter (oil saturation (%), longitudinal structural coefficient of the oil layer, average pore throat radius, gas-oil ratio (t)/m3), brittleness index (%), and minimum horizontal principal stress (MPa)). is the resolution coefficient, generally taken as (0, 1) or taken as 0.5
Summary
According to estimates by the U.S Energy Information Administration (EIA), China’s technically recoverable tight oil resources amount to 44.8 × 1 08 t, ranking third in the world (Zou 2011). According to the geological characteristics and developmental characteristics of using horizontal well volume fracturing, quasi-natural energy development, and that considering only the permeability and oil content cannot accurately reflect differences in reservoir quality, a classification of the Chang 7 reservoir group in the Ordos Basin is proposed. (6) The minimum horizontal principal stress ( h ) is the minimum pressure at which the reservoir rock deforms and fractures along the plane direction under the action of an external force on the formation and reflects the difficulty of rock fracturing This evaluation parameter system combines key parameters, such as oiliness, seepage characteristics, initial energy, and rock mechanical characteristics, and can effectively reflect the difference in sweetness development of the Chang 7 oil group
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