Accomplishments and Challenges of Horizontal Well Technology in Hassi Messaoud Oilfield

Abstract

At present, about half of Hassi Messaoud field output is being produced from hundreds of non-conventional wells. Two horizontal well (HW) applications are being used; new infill medium-radius horizontal wells in between productive zones and re-entry of dry-to-poor vertical producers all over the field using short-radius equipment. The purpose of both projects is to recover incremental oil from poor-quality reservoir parts in order to boost overall production and improve oil recovery. Horizontal well technology has proven to be a good alternative to overcome reservoir areal heterogeneity and intercept natural fractures when present in the reservoir. Although the two techniques have significantly improved production from marginal areas, several limitations and problems still have to be addressed. Challenges include weaker-than-expected productivities, rapid production decline rates in most wells, difficulties in data acquisition and inadequate completions for both remedial stimulation and zonal isolation. This study attempts to bridge production profiles with well and reservoir parameters such as; well length, permeability, vertical communication, lateral heterogeneity and anisotropy, near wellbore damage, pressure support,…etc. The article presents a comprehensive analysis of horizontal wells in the field and investigates many aspects of the observed success and failure cases. It also discusses the benefits of underbalanced drilling and pre-perforated liner completions. By benchmarking current well performances, the paper draws some suggestions for well design and completion strategies for prospective wells. Introduction The Hassi Messaoud reservoir has been on stream since 1958. Currently, it produces about 65 Mm3/D of 45°API oil from a thick Cambro-Ordovician sandstone formation. The structure is a flattened anticline with a sequence of horts and grabbens contained by faults in a submeridian direction. The faults are generally oriented SSW to NNE and cross the entire reservoir. The depositional environment is fluvial at the bottom to marine at the top. The shaly sandstone contains silt interbeds which have a thickness between 0.2 and 0.4 m with a metric to kilometric lateral extension. The reservoir is naturally fractured in some parts because of tectonic activity. Fractures are either open or plugged with materials such as shale, silica, anhydrite, pyrite, and bitumen. The reservoir is subdivided into four distinct formations—Ri, Ra, R2, and R3—in addition to a zone of alternance with Ra-Ri and R2 being the main and secondary reservoirs respectively. The producing Ra-Ri is subdivided into six intervals: D5, D4, D3, D2, ID, and D1. The reservoir has a porosity ranging from 6 to 12 %. Overall, the permeability is low with a range from less than 1 to more than 100 md in open-fissures layers. The reservoir was initially undersaturated with an oil saturation of about 80%. The reservoir was subdivided into productive zones. Most zones are under miscible gas flooding. Five zones are under water injection. Up until 1995, the reservoir was developed using vertical wells. Along with matrix treatments, hydraulic fracturing is extensively used with more than 300 wells already treated to compensate for low permeability or to bypass nearby wellbore damage. Gaslift is used for production activation throughout the field. Pilot projects for horizontal well technology started in the mid 1990s. The objective was to develop the reservoir's areas where conventional vertical drilling deemed unsuccessful. The first application was drilling medium-radius infill wells in lower permeability areas and at the peripheries of zones where heterogeneities are high and reservoir continuity is uncertain. The second technique consisted of re-entering dry-to-poor vertical wells using short radius drilling equipment. In this study we discuss the implementation, lessons learned and challenges of these unconventional wells. Many reservoir and production aspects are also discussed throughout the paper.