Practical Solutions for HTHP Offshore Reservoir Surveillance

Abstract

Chasing new plays often make operators reach to complex and non-traditional reservoirs. Especially, at offshore hydrocarbon discoveries it becomes critically important to characterize the fluid, assess pressure profile and understand the flow behavior. This work is a case history of successfully implemented reservoir surveillance techniques at HTHP offshore green field.The key challenges included presence of high pressure pockets/ panic zones, high cost of well testing with additional slickline & logistics, uncertainties of fluid phase and flow behavior at really tough HTHP conditions. These challenges were addressed by utilizing a flexible mix of modern day technologies. This successful case on reservoir surveillance is elaborated in the present abstract.1. Heavy duty dual packer Modular Dynamic testing: The dual packer formation evaluation tester could withstand 400F and 13500 psi formation pressures; while keeping drawdown in ultra low permeability sandy siltstone. 2. HTHP sour gas Permanent Down-hole Gauges (PDG): The presence of CO2 (nearly 10%) and H2S (110 ppm) with steam fractions was fatal for the wellbore integrity. Use of sour-proof Permanent downhole gauges to actively monitor the BHP & BHT as close to perforations. 3. Extreme performer Production Logging Techniques (Extreme PLT) for Ͼ400F zones: At high temperature he fluid phase behaviour, pay-zone resistivity and thin transition zone is hardly predictable. To overcome the uncertainties of fluid type, hold and thief zones the extreme PLT tools played the judging role.This paper shows insights of learning and how it was utilized as a solution. Huge saving was achieved on accounts of i. Fluid characterization and facility selection, ii. Recognized panic/ pressure inversion zones for future drilling campaign, iii. Saved cost of repeated slick-line operations for well testing by real-time well performance monitoring with PDG.The learning phase was relatively longer but the learned decision added significant value to the project. Use of tools and tailor made combinations made Reservoir Surveillance much easier, cost effective and ultimately reduced the uncertainties. The field has been put on production within relatively shorter timeframe.