Development and Deployment of a "Bullheadable" Chemical System for Selective Water shut off leaving Oil/Gas Production Unharmed

Abstract

A low concentration chemical treatment has been developed for pumping into a producer from surface to stop water production without harming hydrocarbon production. Matrix reservoirs are the primary target, though the upper permeability limit is not yet known. Numerical simulation has shown that while such a treatment would not be universal, many viable targets exist. Horizontal wells and multilaterals can make ideal targets, as would many vertical wells in heterogeneous formations and hydraulically fractured wells. Key performance targets were set for these chemical selective water-blocking systems (often called relative permeability modifiers). A dilute, water-dispersed system was favoured as treatment volumes were expected to be large in some cases. Because some of the chemical will enter valued oil/gas zones, the chemical must collapse to allow oil/gas to flow back through treated rock. A mechanism for this is described. To be of wide use, the chemical system should inhibit water production in reservoir rock with matrix permeabilities up to 10 Darcy, and at temperatures up to at least 110°C. Simulation indicated the minimum degree of water block required for selected targets. However, laboratory tests showed that blocks beyond 99.5% could be slow to clean up to hydrocarbon flow under available drawdown. This gave a performance target range. Well targets should always have appropriate reservoir stratigraphy, but it may not be possible to log the wells pre-treatment to check hydrocarbon/water inflow distribution. Therefore some "high-risk" treatments would fail because of lack of separate oil inflow, or absence of any flow barriers (such as shale) between water and remaining oil. A simple remediation treatment option was therefore required. Also, low toxicity and compatibility with production facilities were seen as non-negotiable properties. We describe the key molecular design parameters derived to give a polymer/crosslinker system with the performance demanded from simulation. Laboratory test results showing the required water/oil block performance and long term stability (at 100 °C) are presented. Field deployment designs including "rule of thumb" treatment volumes are described. The polymer and crosslinker were manufactured at full scale for trial application. Quality assurance tests of this unique "dancing-thin- gel" system are detailed. Results of several full-scale "calibration" field trials are presented. Lab-field correlation appears to be acceptably robust. Introduction Drilling and completion technology has advanced to permit economic development of more challenging reservoirs. Use of multilaterals, extended reach, horizontals, sand-screen/gravel packs, barehole, or sub-sea completions has become common. When these non-conventional wells cut water, they often still have significant production potential. However, access for remedial work such as Water Shut Off (WSO) interventions is difficult and expensive. Further, use of established WSO technologies such as straddles or coiled-tubing (CT) squeezes requires a Production Logging Test to gain knowledge of the water inflow point. Even then there is still a significant risk of failure. A PLT may show where the water enters the well. But it says little about whether reservoir shales are effective barriers to induced crossflow after the water has been shut off. For bullhead WSO, a PLT is not needed to help placement, though it might still help to select lower risk targets.

When and Where Relative Permeability Modification Water-Shutoff Treatments Can Be Successfully Applied

“…These are some of the many illustrative literature references (Sandiford 1964;White et al 1973;Sparlin 1976;Weaver 1978;VanLandingham 1979;Schneider 1982;Kohler et al 1983;Dunlap et al 1986;Dovan and Hutchins 1994;Seright 1995;Stanley et al 1997;Faber et al 1998;Eoff et al 2003a;Ligthelm 2001;Morgan et al 2002;Di Lullo and Rae 2002;Eoff et al 2003b;Kume 2003;Seright 2006a;Pietrak et al 2005) that discuss the RPM phenomenon. These are some of the many illustrative literature references (Sandiford 1964;White et al 1973;Sparlin 1976;Weaver 1978;VanLandingham 1979;Schneider 1982;Kohler et al 1983;Dunlap et al 1986;Dovan and Hutchins 1994;Seright 1995;Stanley et al 1997;Faber et al 1998;Eoff et al 2003a;Ligthelm 2001;Morgan et al 2002;Di Lullo and Rae 2002;Eoff et al 2003b;Kume 2003;Seright 2006a;Pietrak et al 2005) that discuss the RPM phenomenon.…”

Aperture-Tolerant, Chemical-Based Methods to Reduce Channeling

“…40 The goal of these WSO treatments should be to not reduce the permeability to oil flow by a factor exceeding two. 22,39,44 However, for the sake of completeness, it should be noted that Ref.…”

“…40 was used to make this estimate. ) ..................................................................................................... (40) In this equation, L is the distance between wells (300 m or ~1,000 ft), φ is formation porosity (0.261), S or is residual oil saturation (0.28), and Δp is pressure difference between the wells (20 MPa or ~2,900 psi). For most wells examined, the actual polymer breakthrough times (6 to 8 months) were reasonably consistent with the times calculated using Eq.…”

Innovative, Integrated, and Cost-Effective Chemical Management on the Miller Platform

“…This requirement has been fulfilled with the application of selective water shutoff systems (Morgan et al 2002). These systems are chemical treatments bullheaded from surface through the production tubing into the formation.…”