Evolution of Frac-Pack Design, Modeling and Execution in the Ceiba Field, Equatorial Guinea

Abstract

Proposal The paper details a study of 15 fifteen frac-packs in twelve wells in the Ceiba Field, offshore Equatorial Guinea.Initial frac-packs were very unpredictable, experiencing numerous early wellbore screenouts and unpredictable tip screenout (TSO) behavior, placing proppant volumes of 10 to 160 klb with TSO net pressure increases ranging from 100 to 1,500 psi. The goals of this study were to:develop a fracture modeling approach that would more reliably predict TSO behavior using mini-frac data,develop reliable mini-frac analysis procedures anddetermine the primary cause(s) of the early wellbore screenouts. The study resulted in improved designs, better execution procedures, more predictable TSO behavior and a reduction in early screenouts. After reliable analysis procedures were developed, it was clear that mini-frac fluid efficiency and net pressure varied dramatically in the Ceiba frac-packs, with efficiencies ranging from less than 5% to over 30% and net pressure ranging from 170 to 900 psi. After reviewing rock mechanical data and evaluating various fracture modeling approaches, the variations in net pressure were attributed to complex fracture growth due to high wellbore deviation and long perforated intervals (as opposed to differences in modulus). The combination of consistent mini-frac analysis procedures and a fracture modeling approach that included fracture complexity resulted in a much more reliable prediction of TSO behavior. Introduction The Ceiba Field is located offshore Equatorial Guinea (Figure 1). The oil productive interval is characterized by a 100- to 650-ft section of laminated sand-siltstone-shale sequences (8,200 ft TVD). Well deviation through the pay ranges form from near vertical to 60 degrees. There are several high permeability but poorly consolidated sands targeted for frac-pack completion, with permeability ranging from 100 to 1,000 mD.[1] Overview and Objectives of Frac-Pack Evaluation. A comprehensive evaluation of Ceiba frac-pack treatments was performed to improve completion performance. The objectives of the evaluation were to:Develop a calibrated fracture model that would accurately match actual treatment behavior and reliably predict TSO behavior using mini-frac data.Develop an Excel database that contained fracture treatment information, mini-frac results, completion details, reservoir properties, fracture modeling results and treatment analyses that could be used to improve future designs and real-time job design changes by providing easy access to previous mini-frac analyses and treatment schedules, while also providing a platform for treatment evaluations.Develop consistent and reliable mini-frac analysis procedures.Identify the primary factors that cause premature wellbore screenout to allow future designs and/or completions to be altered to improve treatment success and reducing premature screenouts.