Water Shut-Off Through the Use of Advanced Thermal and Acoustic Models
Authors: Yurchenko Andrey , Fesina Yulia 
Published: December 2024

Since early 2010s’, horizontal drilling has become the standard practice in developing oil and gas production capacities – it amounts for over 80% of production capacities in USA alone. However, despite countless improvements in technology, many operators are seeking additional insights into explored reservoirs, as lateral wellbores pose numerous challenges, especially when introducing water. Horizontal wells have a larger contact area with the reservoir compared to vertical wells, which means they are more likely to encounter water-bearing zones. This can happen if the well is drilled too close to the oil-water contact (OWC) or if fractures extend into aquifers during hydraulic fracturing. Once water breaks through into the well, it often dominates the production stream, reducing oil production. Managing this water influx is difficult as it tends to flood the wellbore quickly, leaving oil bypassed in the reservoir.

Conventional production logging tools (PLTs) often struggle to accurately measure flow in these wells. Horizontal wells often experience complex multiphase flow, with oil, gas, and water moving simultaneously along the length of the wellbore. Unlike vertical wells, where gravity helps separate fluids, production in lateral wellbore may encounter stratified or slugging flow, where fluids move in irregular or uneven patterns. This is further complicated as inflow is often not uniform along the length of wellbore. Different sections of the well may intersect zones of varying permeability, pressure, and fluid content, leading to some parts of the well contributing more significantly to production than others. The presence of different phases at different points in the wellbore can distort measurements, diminishing accuracy of production allocation.

Temperature readings acquired via PLT logging, or Distributed Temperature Sensing (DTS) are also limited, this time by the complex geometry of geological structures involved in the reservoir drainage. Acoustic measurements can provide insightful information about active reservoir contributions but are mostly used at qualitative level as they are generally insensitive to phase of produced fluid. In addition, acoustic spectrum in low to intermediate frequencies is saturated by signals from both the reservoir and completion flows.

To circumvent these limitations, the proposed method of analysis must a) identify active reservoir contributions at formation level (which includes behind installed casings), b) delineate between water and hydrocarbons inside the wellbore, and c) characterize reservoir contributions by their respective phases.

These requirements are achieved through the use of Advanced Thermal and Acoustic Models (ATAM). ATAM technique is aimed to bridge the gap in horizontal wells where reliable identification of water ingress is difficult. Those cases include horizontal wells with complex lithology, high degree of reservoir compartmentalization, wells with extensive fracture networks, and Steam Assisted Gravity Drainage (SAGD) operations – all with marginal (≤ 10% or ≥90%) water cuts. Whilst existing logging technique (PLT) identifies the area of fluids ingress to inner completion, the ATAM expands this knowledge by allocating reservoir flow units (Acoustic Modeling) that produce them. Consequently, the use of Advanced Temperature modeling coupled with High Precision Temperature (HPT) breaks down contributing reservoir units at a higher granularity: single flow interval can be composed of several thin sub-units, each with their own productivity.

This paper outlines an additive approach to reservoir characterization through the use of Advanced Thermal and Acoustic Models to identify the source and conditions leading up to water ingress in hydrocarbon wells. This in turn provides asset operators with targeted knowledge for perspective remediation work.