High-Definition Deep-Looking Inversion Integrated Service Set Golden Spikes to Push Lithological Reservoir Development Limit
Authors: Gao Xiaofei , Wu Yuze , Shen Xu , Dai Ling , Chang Botao , Wang Chao , He Chengwen 
Published: November 2018

Development of lithological reservoirs is becoming vital in the Pearl River Mouth basin of the South China Sea. One of these is the Neogene M lithological reservoir in which the deposition of a paleodelta over multiple periods caused a complex profile including severe heterogeneity, rapid lateral property change, poor sand connectivity, and irregular thickness variation (0.5 to 12 m) with interbeds. The current development scope is approaching the predicted eastern sand-pinchout line, making it necessary to identify key points as "golden spikes" to shape the sand bodies’ spatial distribution profile, internal characterization, and pinchout points. based on the sand bodies’ distribution network, drilling and production techniques can be specifically configured to push the development limit as much as possible by efficiently squeezing remaining oil.

In the horizontal well campaign, five appraisal wells are important golden spikes where interwell structural and stratigraphic uncertainties are high due to limited resolution of 3D seismic and sequence stratigraphic data and limited depth-of-investigation (DOI) of conventional logging data. A high-definition deep-looking inversion service was identified to balance resolution and DOI. This novel inversion stochastically analyzes hundreds of formation models using the Metropolis-coupled Markov-chain Monte-Carlo method and then identifies multiple layers (more than three) with 6 m DOI, formation resistivity, anisotropy and dip. With the key resolution-DOI balance, this deep-looking inversion can reveal high-definition interwell details and set a series of golden spikes to identify sand superposition configuration and pinchout points. Within the refined 3D reservoir model, the geo-steering efficiency, completion configuration, and waterflooding stimulation efficiency could be optimized for maximum recovery. Furthermore, a reasonable well pattern arrangement could be developed to sweep the predicted remaining oil and progressively push the development limit.

As evident from ten horizontal wells, high-definition interwell reservoir details were revealed by describing up to four boundaries and five layers simultaneously within maximum 5-m distance from borehole. The golden spikes characterized sand bodies’ profile and their pinchout points. Compared to the prognosis, the southeast margin has been moved to the west. Smooth trajectories were proactively steered to chase irregular sand bodies with minimal loss. Based on the refined 3D reservoir model, proper completion configurations were designed to accommodate the variable properties in this reservoir. One horizontal water-injection well focused on specific discontinuous sand bodies for an average 1.6MPa (megapascal) /well pressure recovery and total 126,000 barrels/year incremental oil. Oil recovery reached 13% within 3.5 years of production, faster than the prognosis. Under current development led by this integrated service, four wells were planned towards updated eastern pinchout line to exploit the remaining oil as much as possible. With increasing distance from the platform, laterals can be placed accurately to achieve objectives with high drilling efficiency and less drilling risk by minimizing unnecessary trajectory adjustments.

From resolution-DOI balance to the identification of golden spikes, this deep-looking inversion could constrain 3D seismic and sequence stratigraphic interpretation to refine the large-scale reservoir model. Considering drilling and production methods, this integrated service could effectively push the development to the potential limit.