Comprehensive Workflow of Matrix Acidizing Design and Analysis in Multi-Layer / Multi-Zone Reservoir - Offshore Case History

Zareiforoush, Ali (KPE Upstream Subsidiary of OIECGroup) | Safari, Alireza (Mehran Engineering & Well Services Company) | Momeni, Ali (KPE Upstream Subsidiary of OIECGroup)

OnePetro 

Abstract

In this paper we present details of the approach utilized to optimize the well stimulation campaign in the continued development of a huge carbonate gas condensate field in the Offshore Iran. This study discusses what have been done differently, best practices, and learning. What is different in this campaign from previous ones?

Detailed design

Detailed well-by-well review

Fundamental data collection for parameters analysis - operational, subsurface, treating fluid data

Data management system allowing for quick access

Design tool for detailed damage diagnosis, fluid system selection, pumping schedule design, and pressure matches.

QA/QC and compatibility tests aiming to obtain high success rate.

Challenges

High contrasts in porosity, permeability and initial pressure

Complex mineralogical & lithology composition

Fissures and Vuggy porosity

Long perforated intervals and well inclination effects

Pre-acid nearwellbore reservoir initial condition

High rate and ΔT effects on completion & cement integrity

Objectives

Optimum zonal coverage

Keep completion integrity while high rate injection

Use minimum volume of chemicals

Reduce operation risks & costs

Optimum acid placement in bullheading treatment in commingled mode is still the challenging issue in in Iran well stimulation jobs. We propose a comprehensive step-by-step workflow to get the best results using Nodal Analysis & Stimulation Software in a logical way described later in the text. Diversion techniques history in this field is: Mechanical diversion, Ball sealers, Selective perforation with polymer based diverter, Selective perforation with high injection rate and VDA technique. Our new diversion method that deployed along with a revised placement model, field calibrated to more accurately predict treatment pressure responses, to optimize acidizing design and to maximize diversion in this layered reservoir, studied in this paper.

Results presented include stimulation treatment plots alongside model post treatment pressure matches, pre and post stimulation production logs, clean up data and well test interpretations to validate the models. We describe high/low permeability, multi zone treatments with a bullheaded matrix acidizing technique. We observed in one well through tubing treatment pressures response and oscillate between 2000 and 3500 psi, far above what is typically observed in this field in which the pressure reduction happened quickly from 3000 to 1000-500 psi.

We conclude that due to enhanced diversion results in uniform zonal depletion which is due to uniform zonal acid coverage. We have also found operational benefits in deploying the system in that commingled zones, normally perforated and stimulated in several stages can now be easily and effectively stimulated using a one-stage technique.