Integrated Approach for the Horizontal Well Design and Geosteering in Thin Jurassic Sands

Abstract

The objective of this article is to describe integrated approach, including planning and reasoning of well constructions based on field development modeling, calculation individual well trajectories taking into account full complex of knowledges in target formation geology in drilling area and well placement service usage at the drilling stage to elaborate formation geology and achieve planned well production. Results of horizontal sections trajectories planning are shown in this paper, as well as description of geosteering process features. Results of well positioning optimization, based on hydrodynamic modeling were used of well trajectory planning, as well as complex of geological information: structural surfaces, well-to-well correlation, fluid contacts, seismic profiles with inversion results and sector model for the drilling area. Well placement service at the drilling stage allowed to significantly decrease risks related to lithological and structural uncertainties and, therefore, maximize effective length of horizontal sections keeping total length fixed. Following measurements were used during the job: D&I (direction and inclination); GR, resistivity, neutron-density logging and density image. Those data were utilized for 2D structural model update and adjustment. Choice of optimal well trajectory for horizontal section effective length maximization in target sandstone reservoirs with low thicknesses and low permeability, along with well placement service usage resulted in significant well production increase. BHA with LWD tools, that was designed taking into account specific geological and technological conditions, was found as most appropriate for well placement methods sufficiency and determination of reservoir properties and saturation. Geological model adjusting during geosteering at the drilling stage allowed to achieve maximal NTG (net-to-gross ratio). A total of 19 horizontal sections were drilled for field development with cumulative total length more than 23,000 m and cumulative effective length more than 16,000 m. As a result of such approach, wells have productivity that exceeds planned. Final result of well drilling is gas production rate from 300,000 to 700,000 m3/day (summarized production rate is up to 3,000,000 m3/day). Integrated approach and close interaction between companies involved at all stages of well planning and drilling resulted in significant decrease of risks related to structural and lithological uncertainties. Increase of horizontal sections effective length had effect in production increase and, therefore, allowed to improve rate of return on investments.