An Industry Consortium (BP, ChevronTexaco and Nalco Company) conducted a joint research project known as Bright Water. The goal of this project was to develop a novel, time- delayed, highly expandable particulate material that would improve the sweep efficiency of a water flood. In November 2001, the first of these water flood profile modification treatments was pumped in the Minas field, as reported in SPE 84897 (1). An overview of the development of the particulate system is given in the present paper. The polymeric "kernel" particles are capable of "popping" under the influence of temperature and time. The expanded particle can then provide resistance to fluid flow in porous media. Various properties of the kernel dispersions are summarized. Laboratory tests representative of the deployment of the product are presented to illustrate the injection, propagation and popping of the particles. Screening criteria for application of the product are reviewed and related to product selection for the field trial. Introduction Over the last 40 years there has been a concerted effort to improve the recovery of oil by mobility control using polymers and polymer derived gels (2). Much of the work has focussed on near wellbore gel treatments using polymers and gels but there has also been considerable work on Polymer flooding and hybrid derivatives of this (3–7). All flooding polymers alter the water mobility in the reservoir predominantly by changing the aqueous viscosity. The ratio of the apparent viscosity of the treatment (as calculated from pressure measurement during treatment injection) to the viscosity of water in the same conditions is known as the Resistance Factor (or RF). Some polymer can also adsorb on the rock pore walls to leave a lasting change through altering the hydraulic radius of the pores and thus the permeability of the rock. The ratio of the effective permeability of the rock pores to water flow before treatment to the effective permeability after flushing the treatment out is known as the Residual Resistance Factor (or RRF). The polymer flooding process has some strengths, but also a number of weaknesses. In particular the polymers are sensitive to salinity, temperature, shear and biological degradation to differing degrees. The better performing polymers tend to use more expensive monomers or production processes. There are also limitations related to the reservoir flooding process. High viscosity of the polymer flooding solution limits the injection rate at any given injection pressure. The maximum usable viscosity is typically limited to between three and ten times that of the injection water (RF maximum of 10). There are added risks of the injector fracturing and of polymer shear degradation. Unfortunately, the effectiveness of the process is reduced at low viscosity, and overall this severely restricts the range of viable applications. In the field projects where polymer flooding has been used with technical success, the cost of the accelerated oil is relatively high. In 1996 it was estimated as $8 to 10 per barrel (8) but more recently a review of the field wide commercial polymer flood in the Daqing oilfield (5) found that in this mature field, with easily accessible fresh water, the fully accounted cost was $9.34 per barrel compared with $9.42 for continued water flood production. It is apparent that a less restricted, more cost effective method for improving sweep efficiency in oil reservoirs would be desirable. This could be achieved by injecting a low viscosity material, which subsequently triggered to form a highly viscous or blocking phase. Concentrating on the permeability reduction element of the waterflood modification should result in a system that uses most of the injected materials to produce a lasting effect. It would also ensure that injected material was never subsequently produced with the water from the field. Field trials and commercial applications of gel systems intended to achieve this have been reported (9,10) but it is unclear how far the gelant penetrates into the reservoir (11).

An Industry Consortium (BP, ChevronTexaco and Ondeo Nalco Energy Services) conducted a multi-company research project known as Bright Water. The goal of this project was to develop a time-delayed, highly expandable material that would improve the sweep efficiency of a water flood. In November 2001, the first of these water flood profile modification treatments was pumped in the Minas field. The Minas Field, located on the island of Sumatra in Indonesia, has an OOIP of 8.7 billion barrels, is at nearly 50% recovery, and has water-cuts greater than 97%. Reservoir thief zones have been identified throughout the main reservoir layers. The main objective for pumping a profile modification material is usually to divert injected water out of thief zones and into zones with higher oil saturation, though areal sweep improvement can also be expected. The profile modification treatment of 42,000 barrels water containing 4500 ppm of active material was pumped into Minas injector 7E-12 ("A1" sand). The objective of the field trial was to verify that significant volumes of this low cost material could be pumped deep into the reservoir at low viscosity, and then expand after a pre-designed time interval. Injection tracer studies were conducted pre- and post-treatment to aid in determining changes to the injection sweep efficiency. A bottom hole pressure fall off test was also used to measure post - job permeability. The trial demonstrated that large volumes of the material can be pumped into the formation without raising the injection pressure or blocking the injection well bore, can propagate in the rock pore system, and then will expand at a pre-designed time. Changes in oil production after the trial will be discussed along with the field data acquired during and after the trial. As part of the continued development of this material, a second trial commenced in late November 2002 on a North Sea (UK) production platform. The treatment was successfully placed in mid December, 2002. Introduction This paper presents a case history in which a novel profile modification treatment was pumped in the Minas waterflood. Of all the problems that can beset oil wells, unwanted water production is one of the most troublesome, yet water flooding to improve the recovery of oil is the most common secondary recovery process used in the modern oil industry. Water production causes many problems such as corrosion, scaling, cost of oil water treatment and cost of disposal. In water injection projects excess water production is often linked to poor sweep efficiency, which renders significant amounts of oil irrecoverable during the economic life of a field. Poor sweep efficiency can be the result of zones with unfavorable permeability in heterogeneous reservoirs or unfavorable mobility ratio within homogeneous rock. Specifically water can break through from the water injection to the oil production wells in the most permeable zones while significant oil is left in the reservoir (Fig. 1) or it can pass through low mobility oil by a process of viscous fingering.1 The problem can be even more severe when bottom water zones with high water saturation and therefore variations in relative permeability exist. 2,3

Objective The objective of this study was to identify clinicopathologic features that are associated with an increased risk of recurrence for borderline ovarian tumors (BOT). Methods We performed a retrospective review of all patients treated for BOT at our institution from 1979–2008. Progression-free survival (PFS) was defined as the time of diagnosis to time of recurrence/death or last follow-up. The Kaplan-Meier method was used to calculate the PFS rate and Wilcoxon Gehan test was performed to identify prognostic factors. Results A total of 266 patients were identified. The median age was 43 years (range 15–94 years). The majority of patients (68.4%) had FIGO stage I disease and serous histology (73.7%). Only 23 (8.6%) patients developed recurrent disease. The median PFS was 19 years and the median follow-up was 4 years. Abnormal baseline CA-125 (>35 U/ml), advanced stage, age at diagnosis, and invasive implants were associated with decreased PFS. Of the 196 patients with serous BOT, those with a micropapillary pattern had a 3-year PFS of 75.9% (95%CI 55.6–87.8) compared with 94.3% (95% CI 88.4–97.3) for patients without micropapillary pattern (P<0.001). Conclusion Age at diagnosis, an elevated preoperative CA125, invasive implants, and micropapillary histology were clinical factors associated with increased risk of recurrence in women with BOT. Including these clinicopathologic features will likely identify patients at higher risk for recurrence, for whom development of new treatment strategies would be appropriate.

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