Reservoir simulation, ion reactions and near-well bore modelling to aid scale management in a subsea Gulf of Mexico field

This paper presents the findings of a study into the impact of reservoir flow behaviour on both the scaling risk at production wells, and the options for managing this scaling risk, for a deepwater sandstone reservoir in the Gulf of Mexico. One significant feature in this field is that flow takes place through isolated formation layers, and choices made regarding the seawater injection wells have a great impact, not only on the BaSO4 scaling tendency, but also on the placement of scale inhibitor squeeze treatments in the producers.
In addition to seawater injection, oil production is supported by the aquifer. The first stage of this study involved identifying the split between connate, aquifer and sea water in the produced brine. This provided data that could be used to calculate the evolution of the scaling risk over the lifecycle of each well. The formation brines contain barium and the injection water if full sulphate seawater and the relative proportion of each brine, the water production rate, and pressure and temperature conditions all determine the scaling risk.
The evaluation of the extent of ion reaction between the injection water (sulphate) and formation water (Ba) from injection to production well can result in a significant reduction in the available barium within the produced water and hence the scale risk/scale inhibitor concentration required preventing disposition. In this study as the injection wells were completed with inflow control devices (ICD’s) it gave the opportunity to manage the injection split via these ICD’s, not only to improve sweep efficiency, but also to balance reservoir pressures and make squeeze treatments more efficient. The study will present the squeeze treatment volumes and estimated treatment lifetimes possible for two scenarios for the water injection application to this deep-water field.
The implications of this type of study will be highlight in terms of the economic option that this data allows an operator to consider prior to commissioning water injection in these challenging environments.