Performance Evaluation of Horizontal Wells in Thick Oil Column of Greater Burgan Field
Authors: Chakraborty Paban Kumar , Bhattacharya Muktibrata , Gazi Nazmul H. , Morad Raed H. 
Published: February 2016

The Greater Burgan field located in South-Eastern part of Kuwait is producing around 90% from the Third Sand clastic reservoirs and is considered as swing producer. This Lower Cretaceous Third Sand Middle has excellent lateral and vertical flow system without persistent flow barrier. Horizontal well plan was targeted on this sand in areas of significant oil columns in structurally favorable areas for optimum oil production without significant drop of reservoir pressure. Exploitation of oil from this high permeability sand over the years has resulted coning, fingering, non-uniform fluid flow resulting by-passed oil pockets. An integrated reservoir management plan consisting of both vertical infill wells for production from multi-layered sands and horizontal wells for middle third sand has been conceived to effectively sweep the oil. Thirteen horizontal wells have been drilled so far in oil columns varying from 80 ft to 150 ft. The perforation intervals in the horizontal section vary from 1100 ft to 2330 ft in order to achieve maximum reservoir contact area for sustained significant dry production.

The horizontal wells have provided significant insight into the lateral heterogeneity of this sand affecting oil contribution. The completion of these wells involved perforating vertically upwards in the direction of highest stress to minimize sand production and to complete mostly as under-balance for improved well bore cleanup. Production Logging was carried out in eight wells.

This paper highlights the challenges in designing and completing successful horizontal wells in the Third Sand Middle formation of the Burgan Field. Also discussed is the critical understanding of oil entry mechanism from the flow profile under very low drawdown pressure. The close monitoring of multiphase fluids flow patterns, both in offset wells and within the well bore, is also described.

Introduction

The Greater Burgan Field, shown in Fig. 1, lies on the onshore in the southern part of Kuwait. This oil field was discovered in February 1938. Initially the production came from Wara sandstone and soon followed by underlying Burgan clastic reservoirs. The Burgan reservoir mainly consists of three reservoir units namely Wara, Third, and Fourth sand. The Third and Fourth sand members have excellent reservoir characteristics and are prolific producers. However, at this time the Third sand is the major producer, contributing presently around 60–70% of the total production from the Greater Burgan field. This field is the swing producer and life line of Kuwait.

Fig-1 Location of Greater Burgan Field

The sustained demand to enhance dry oil production due to facilities constraint, inaccessibility of reserves through vertical wells, coupled with coning problems in some existing wells, has resulted in unconventional thinking of drilling non-conventional horizontal wells in this massive sandstone reservoir unit. Horizontal well drilling program was launched in this field in the later half of 2005. The success of the first two wells in the crestal part of the Burgan dome provided further fillip to continue drilling more horizontal wells in this thick Third Sand Middle reservoir. These wells were completed in this sand with varying horizontal sections. As of today 13 wells have been drilled which accounts for about 10% of the total production from the field.

Geology

The Lower Cretaceous Burgan Formation is equivalent to late Albian-Aptian Nahr Umr formation of Southern Iraq, Qatar, and United Arab Emirates (Fig.-2). The reservoir quality of the sandstone improves from north to south in the Burgan Field. The spatial variation of reservoir continuity was the result of sea level fluctuation and sediment supply.1