Life-Cycle Profile Control in Subhydrostatic Wells of South Oman

Abstract

Profile modification of injection and production wells is of major importance in South Oman heavy oil reservoirs. This is because injected and produced water must be controlled to optimize reservoir sweep and oil production. Profile control in artificial lift wells is also a common dilemma because the intervention involves re-completing wells to achieve logging-while-pumping necessary for detecting unwanted intervals. In 2004, two completion philosophies were adopted to allow hoist-free re-entry as well as provide a cost effective life-cycle solution. One is the replacement of smart wells with segmented horizontal wells. This completion allows for effective diagnosis and isolation of watered-out sections. The other is replacing the upper completion of producers in sub-hydrostatic reservoirs with dual Christmas Trees. That makes it possible to measure the inflow profile while pumping through the second tubing. A proactive measure was taken by field-testing a new technology capable of satisfying all basic requirements. The technology is a wireline deployed rubber and carbon fiber sleeve expanded by hydraulic pressure to set flush against the casing. Heat is applied to polymerize the resin before deflating and retracting the running tool. The patch thickness can withstand both burst and collapse pressures, leaving sufficient internal-diameter in 7-in and 4 ½-in casing for subsequent deeper intervention. Phase-1 trial was successfully completed in 3 water injectors late in 2004. Phase-2 trial which was planned for 2 oil producers are still being mobilized and will be executed in third quarter of 2005, late for publication in this paper. Some unique characteristics of this technology made it attractive; namely (1) ability to deploy via smaller size tubing to expand & set in larger perforated liners, thus eliminating rig/hoist requirement, (2) high depth precision using CCL correlation, (3) possibility of bypassing existing patch to isolate downstream toe area, (4) possibility to by-pass isolated areas to re-perforate lower zones and safely retrieve the bloated gun barrels, (5) applying gentle and even hydraulic force contour-to-contour to set against un-reinforced liners, (6) cost effective solution of higher success rate compared to chemical treatments. The trials proved to be the first campaign of its kind to be successfully completed with 100% success rate, while meeting all expectations. Introduction As part of the new effort to reverse the trend of increasing water cut in Petroleum Development Oman (PDO), both mechanical and chemical profile control initiatives have been widely pursued in the Southern and Northern Directorates. PDO currently produces 630,000 bbl/d of oil with about 3.6 Million bbl/d of water - 85% water cut (WC) - and this is expected to remain on the rise unless life cycle remedial solutions are implemented to mitigate this trend in both the existing and new wells. Southern & Northern Oman Directorates are predominantly sandstone and carbonate formations respectively, meaning that their development challenges and costs are somewhat dissimilar. Also, formation & reservoir fluid properties are known to vary widely from North to South. Due to these differentiating qualities, a viable optimization solution in the South might not be found optimal in the North and vice-versa. For example, the South mainly employs a lot of Beam (Rod) Pumps and some Electric Submersible Pumps (ESPs) while the North depends mainly on Electric Submersible Pumps (ESP) and Gas Lifts. While these directorates are currently operated as two different business units in terms of development methodologies, optimization techniques, etc, they however share one common goal of maximizing production at a reduced operating expenditure. The primary aim being to restore oil production to 800,000 bbl/d over the next few years.

Inflow Profile Control in Horizontal Wells in a Fractured Carbonate Using Swellable Elastomers

“…If a completion is run with 4 ½" liner and EZIP packers with perforated or blank pipe over the inflow segments ( Figure 6), then any future inflow profile modification will require a work over of the well with a hoist or coiled tubing unit to either pump chemicals or to install packers or patches [8].…”