Koksal Cig

Improvements of Sampling and Pressure Measurements with a New Wireline Formation Tester Module in Carbonate Reservoirs

A multilayer hydrocarbon reservoir in Abu Dhabi land is in an appraisal stage before experiencing an extensive field production operation. The hydrocarbon reservoir, having medium to low permeabilities, consists of a number of carbonate layers with their associated oil-water contacts. One of the challenges is to sample hydrocarbons in tighter layers as well as to measure valid reservoir pressures to determine oil-water contacts. While the goal is to accomplish the objectives with wireline formation testers (WFT) in openhole conditions, stationary times during logging are limited due to wellbore conditions. The time limit has been a longstanding challenge in the layers having especially lower permeabilities (<1md). A typical sampling operation involves advanced modules of WFT including a Dual-Packer and an Insitu Fluid Analyzer to identify fluid types and provide downhole compositions with densities. Reservoir pressures are measured generally with Single-Probe modules. The new WFT inlet module is introduced first time in Abu Dhabi across the carbonate formations to accelerate the stationary operations. The new inlet module showed an improvement over a Dual-Packer and a Single-Probe modules in several aspects: (1) Stationary times during sampling are reduced due to very low interval volumes in comparison to a Dual-Packer module and up to 60% faster oil breakthrough times are achieved. (2) Tight zone pressures are measured as fast as a Single-Probe module with lower supercharging effects. (3) Set and retract times are shortened so that a new sampling method of a set-retract-reset is developed without exceeding stationary times. This paper summarizes the recent achievements by reducing risks associated with long stationary times. The field benefits are demonstrated in two separate WFT operations by comparing data qualities and job efficiencies in the same reservoir layers. Results show faster sampling, more accurate pressure and permeability measurements in the carbonate reservoir. Introduction The Abu Dhabi land field is a newly developed field located approximately 260 km south of Abu Dhabi city. It has an oil production target of 30000 BPD and will start producing from 2013 as planned in phase I. The field has several carbonate sequences each having its own oil-water contact (OWC), fluid and rock properties. In order to identify OWCs and obtain fluid compositions, extensive reservoir characterization has been underway. The reservoir consists of a layered carbonate system with medium to low permeabilities with heterogeneities. There have been difficulties identifying hydrocarbon in certain layers due to low resistivity signature in the rock. The challenges also extend to establishing pressure gradients although virgin formation pressures are expected in the field. This is solely related to formation tightness. Due to carbonate related challenges, special openhole logs as well as wireline formation testers (WFTs) are run in the field to delineate such formations. The data gathered with WFTs deliver pressures with zonal mobilities, examine layer barriers, collect samples and provide real-time detailed compositions. Interval Pressure Transient Test (IPTT) provides vertical and horizontal permeabilities. Geomechanical properties such as minimum horizontal stress, closure and breakdown pressures are obtained from Stress Testing analyses (Ayan 2001, Ayan 2012, Zimmerman 1990, Pop 1993, Kuchuk 1998, Mullins 2008, Mullins 2010).

Production Logging in Difficult Well Configurations

Production logging is difficult in complex well designs such as horizontal multilateral (ML) wells with jagged level-two exits. The ML exits can obstruct the access of logging tools due to damage around the milled windows. Once inside a low-flow high-water cut reservoir, the challenge becomes measuring an oil inflow profile in stratified flow.