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Abstract
Shale oil and gas fields usually contain many horizontal wells. The key of 3D structural modeling for shale reservoirs is to effectively utilize all structure-associated data (e.g., formation tops) in these horizontal wells. The inclination angle of horizontal wells is usually large, especially in the lateral section. As a result, formation tops in a horizontal well are located at the distinct lateral positions, while formation tops in a vertical well are usually stacked in the same or similar lateral position. It becomes very challenging to estimate shale layer thickness and structural map of multiple formation surfaces using formation tops in horizontal wells. Meanwhile, the large inclination angle of horizontal wells indicates a complicated spatial relation with shale formation surfaces. The 3D structural modeling using horizontal well data is much more difficult than that using vertical well data. To overcome these new challenges in 3D structural modeling using horizontal well data, we developed a method for 3D structural modeling using horizontal well data. The main process included 1) adding pseudo vertical wells at formation tops to convert the uncoupled formation tops to coupled formation tops as in vertical wells, 2) estimating shale thickness by balancing the shale thickness and dip angle change of a key surface, and 3) detecting horizontal well segments landing in the wrong formations and adding pseudo vertical wells to fix them. We used our improved method to successfully construct two structural models of Longmaxi–Wufeng shale reservoirs at a well pad scale and a shale oil/gas field scale. Our research demonstrated that 3D structural modeling could be improved by maximizing the utilization of horizontal well data, thus optimizing the quality of the structural model of shale reservoirs.
Highlights
After over 20 years of the rapid development of hydraulic fracturing in horizontal wells, many shale oil and gas fields exist, most of which are in the United States, Canada, and China (EIA, 2019; IEA, 2019)
The uncoupled formation tops are the main reason for the abnormal thickness in the constructed 3D structural models
Our method is to add pseudo vertical wells (PVWs)-As at all formation tops in horizontal wells and infer the formation tops in all PVW-As based on the thickness of shale layers
Summary
After over 20 years of the rapid development of hydraulic fracturing in horizontal wells, many shale oil and gas fields exist, most of which are in the United States, Canada, and China (EIA, 2019; IEA, 2019). For 3D structural modeling, formation tops are the predominant data. The horizontal well formation top data have distinct features compared to vertical wells due to the large inclination angle of horizontal wells (Figure 1). The horizontal location of formation tops in one horizontal well is far from each other, while it is the same or similar in vertical wells (Figure 1). This raises new challenges for constructing a 3D structural model of shale reservoirs (Wang et al, 2018a; Qiao et al, 2018; Long et al, 2019; Shu et al, 2020)
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