Drilling Optimization In Deep Horizontal Wells
Authors: Portillo Oscar Enrrique , Al-Jahwari Mohammed Hamed , Nasrummnallah Muhammad , AlSharafi Mohamed , Al Maashari Badar , Al-Zakwani Rashid Said , Bugni Michael 
Published: May 2016

In northern Oman, a project for twelve horizontal wells required drilling optimization in a field that presented various geological, drilling, and well construction challenges, including inter-bedded shales, abrasive reservoir, severe stick/slip, sidetracking issues, and low rates of penetration (ROP).

The well design planned for the 12 1/4-in. and 8 3/8-in. vertical sections, building from vertical to a 15° inclination to sidetrack at 8 3/8-in. and landing followed by a 6 1/4-in. lateral

Several collaborative drilling practices and technologies were implemented in the 12 1/4- and 8 3/8-in. vertical sections and the 8 3/8-in. curve section. In the vertical sections, ROP was increased by introducing a closed-loop vertical drilling system with motors and by optimization of bit and BHA design, which also improved run length. The pilot hole was deviated from vertical to facilitate sidetracking. The 8 3/8-in. curve was drilled using a point-the-bit rotary steerable system (RSS), and drilling performance was enhanced with a power section to drill in a single run. Deviating to 15° inclination resulted in a 100% success rate in sidetracking. Many options were tried to optimize BHA design, including continuous bit optimization to find the best PDC bit for steer-ability, durability, ROP, and stick/slip reduction.

This optimization approach lead to a total of 7.5 drilling days saved in the AFE. The use of motors and the vertical drilling system saved 1 day of AFE. Using a point-the-bit RSS to sidetrack from a deviated pilot hole and adding a PDC bit for the curve saved an additional 6 days. High quality of the wellbore saved 0.5 days in avoiding a wiper trip and stuck incidents.

The optimization techniques improve the performance of drilling horizontal wells to consistently attain 100% well delivery with a smooth borehole. The method represents a step change in drilling horizontal wells using the fit-for-purpose approach (i.e., optimized trajectory, proven bit, recommended drilling parameters derived from simulations compared to actual) to deliver wells in a cost-effective manner.

Introduction

In northern Oman, drilling horizontal wells is a challenge and requires an optimization approach to address the problems so that excessive drilling and completion costs can be minimized. This optimization approach involved revisit to the field offset wells data, revision to trajectory design and bit selection, drilling fluid and drilling practices in the 12 1/4in and 8 3/8in sections.

This field is in North of Oman and was discovered in 1979, first brought to production in 1981. Most of the reserves present in the field are light oil. They are contained in a 22m oil layer at a depth of 3175m subsea. This specific hydraulic unit also showed low permeability at the sheet sands of the lower Gharif and Al Khlata (LG/AK) reservoirs (sandstone). A significant volume of oil reserves are, in principle, held at shallower horizons in middle and upper Gharif. The target reservoir is primarily the Al Khlata (AK). Fig. 1 outlines the different reservoirs that are targeted in this field.