Effective Multilateral Open Hole Sidetrack Strategy in Thin Reservoir Units for Maximum Reservoir Contact-A Case Study of Onshore Drilling in UAE
Authors: Dutta Ashim , Ahmed Al Hosani Mariam , Alejandro Aranda Jose , Masoud Rashad , Isiaka Jaiyeola Abiodun , Ahmed Baslaib Mohamed , Mohamed Al Bairaq Ahmed , Mohammed Al Hammadi Adel , Ahmad Mubashir , Radman Velimir , El Shahat Ayman 
Published: November 2019

Recently multilaterals wells are drilled in selective reservoirs in ADNOC Onshore fields for development of hydrocarbon gas in Abu Dhabi. The targets are commonly thin multilayered carbonate reservoirs. The development strategy of multilaterals has significantly enhanced the reservoir contact aiding higher drainage. Multilateral wells can significantly reduce well counts while still achieving robust recoveries. Benefits of using multilaterals included the acceleration of gas production and the reduction in CAPEX/OPEX .

The reservoirs are targeted by drilling duel and triple lateral holes. In triple lateral wells, a main horizontal borehole is drilled followed by laterals on either side of the main borehole. There are challenges of drilling multilaterals as the multilayered reservoir subunits are thin and selective drainage is planned in each sub layers in 6" horizontal sections. It is imperative to have a detail well planning with industry standard drilling technology to deliver successful multilaterals.

During the well planning stage the laterals are planned in 60-80deg azimuthally apart from main both, on either side. The laterals drilled by performing open-hole sidetrack from the main bore, which apparently has a challenge of success. During initial stage of the campaign, lessons learnt from applied practices has encouraged an innovative way for successful multilateral drilling.

Wells are landed on top of the target reservoir. 6" horizontal main bore hole is drilled with creating three humps in the initial part of the well trajectory. The humps are high inclination short section of well path with high Dog Leg Severity. These humps are strategically created at selected points with 300- 500 ft gap from each other and are used to kick off open-hole sidetrack of the lateral holes.

Recorded real time inclination (RTI), Image log data and porosity of main bore along the humps are the key factors considered before executing the side track.

MWD-LWD triple combo along with image log are used in the main bore and tools without radioactive source are used while drilling lateral holes to offset the risk of stuck-up of BHA carrying radioactive source tool.

A detailed step wise operational procedure has been identified and introduced for the success of this development strategy. The high-confidence, successful open hole sidetracking strategy has aided maximum reservoir contact in 6" section with minimum risk and rig time and has substantially contributed to offset additional cost and rig time in all the multilateral wells in ongoing gas development drilling.

This multilateral drilling and field development strategy has been a combined effort of geoscience and directional drilling and have paved way for successful open hole sidetrack campaign with proven standard procedures.