Analytical And Statistical Interpretation Of Near Wellbore Damage In The Cooper Basin, Australia
Engineering Honours Degree, 2012
University of Adelaide
Near wellbore damage in petroleum wells, or skin, impairs flow rates and reduces the ultimate recovery of hydrocarbons. A review of Santos‟ process to optimise production from underperforming wells reveals gaps in understanding and quantifying near wellbore damage. Skin is rarely explicitly quantified in the expenditure authorisation for production interventions. Quantifying skin through traditional surveillance strategies of pressure transient analysis and wireline logging requires invasive actions on the well. In mature fields, these surveillance operations can often be more expensive than directly remediating suspected damage. Model-based approaches to quantify skin may be more cost-efficient. This report proposes that enhanced production optimisation could be achieved through rigorous quantification and improved understanding of near wellbore damage.
An analytical wellbore modelling methodology to quantify skin is developed using a well performance modelling package, Petroleum Experts PROSPER. This methodology is applied to a case study of intervention activities performed between April 2009 and June 2012 on eight gas production wells located in the Cooper Basin, Australia. A multi-layer Jones inflow model is tuned against known flow rates to ascertain skin at original, pre-intervention and post-intervention conditions. Analytical modelling of eight case study wells identified dimensionless skin of between 2 and 25 present prior to production interventions. Reperforation activities were modelled to achieve an equivalent productivity index improvement of between 0.08 and 5.4 Mscf/day/psi. No correlation was observed between reperforation parameters and the magnitude of removed skin nor was positive correlation observed between scale composition and the magnitude of production impairment.
Statistical analysis of remediation activities identified that scale deposition is the leading cause of near wellbore damage within the Cooper Basin. The deposition of barite and calcite accounts for half of all near wellbore scale damage. Our results support a hypothesis of barite scale deposition due to the comingling of formation waters from the Toolachee, Epsilon and Patchawarra formations. Analysis of pressure gradients at wells with known barite and calcite scale impairment was unable to identify correlation between static pressure and locations of scale deposition.
This report recommends rigorous estimation of skin as part of Santos‟ production optimisation process. To achieve this, the application of the demonstrated wellbore modelling methodology was identified as a preferential approach in multi-layer wells when compared to production data analysis in Fekete Harmony RTA. Santos‟ capacity to manage scale deposition and identify remediation candidates could be improved through acquisition of Memory Production Logging Tool (MPLT) and Liquid Evaluation Test (LET) data at more frequent intervals.