3D Rate of Penetration Prediction for Horizontal Well Planning

ABSTRACT: Due to high rock strength and formation abrasiveness, horizontal well drilling in deep tight sandstone reservoirs has been challenged by slow drilling, low average bit footage, and excessive number of bit runs. These challenges contribute to low drilling efficiency and high drilling costs. In the rock cutting process with a Pollycrystalline Diamond Compact (PDC) drill bit, many factors affect the rate of penetration (ROP), including formation characteristics, drill bit design, bit wear conditions, drilling parameters and wellbore hydraulics. In addition to pore pressure, in-situ stresses and other formation properties, compressive strength and abrasiveness are the major factors affecting ROP. The bit profile, back rake angle and total flow area of a PDC bit, as well as the bit wear conditions can affect the ROP. Drilling and mud parameters also have a big impact on ROP. Horizontal wells drilled in deep and tight reservoirs have shown very different drilling performance which provided an opportunity to optimize well trajectory plans for improved drilling performance. We developed a predictive model that considers all the major factors that affect ROP, and the 3D ROP model was used for assisting horizontal well planning. Drilling performance in the wells planned with the 3D ROP model was significantly improved which resulted in improved ROP, fewer bit runs and overall cost savings for drilling the horizontal wells. 1. INTRODUCTION Drilling in deep and tight reservoir formations has been very challenging due to low rate of penetration and high drilling cost. These tight formations are typically characterized by low porosity, high rock strength and high abrasiveness. The Barik and Amin sandstone reservoirs in Oman are greater than 4000 m deep and are reported to have unconfined compressive strength (UCS) of exceeding 35,000 psi (Najwani et al., 2013). Formation rock with UCS reaching 40,000 psi and friction angles from 25 to 75 degrees are also reported in another deep formation in Middle East which contains hard and abrasive sandstone reservoirs consisting of irregular, fine to coarse grained pebbles and conglomerates (Simpson et al., 2003). The challenges these hard rocks present to drilling typically include low rate of penetration (ROP), accelerated bit wear which leads to low bit footage, large number of bit-runs and frequent trips (Simpson et al., 2003).