Chemical Consolidation of Sand Propped Fractures in a Chalk Reservoir Offshore Denmark With Enzymatic Calcium Carbonate Scale.
Authors: Morkved Marie L , Knight Craig , Bhagwan Bhagwan , Garcia Algora Alejandro , Zhuang Wenjing , Rohde Hans Christian , Nelson Alexander C 
Published: March 2015

Sand and proppant production pose a safety risk due to erosion, fill of wells and facilities, often resulting in significant deferred production. A number of wells in the Danish offshore sector are currently closed in or beaned back due to proppant production from sand propped fractured wells where proppant is back produced to surface facilities which were not designed with sand handling capability.

A new sand consolidation treatment involving enzymatic calcium carbonate scale has been applied to individual zones downhole to remediate failed proppant fractures. The technology is an environmentally friendly alternative to commonly used resins and has the added benefit of being completely reversible. A detailed coiled tubing program was successfully executed in a harsh offshore environment with numerous challenges including identification of sanding zones, chemical contamination, logistics, and selective downhole placement.

Laboratory testing was undertaken where unconsolidated proppant was treated with the consolidation chemicals. These results provided important input for defining the placement strategy and indicated that results could be replicated in the field.

Successful results have been achieved from this industry first application of enzymatic calcium carbonate scale to consolidate sand propped fractures in a chalk reservoir. The field application supports the laboratory results, where sand free production of over 700 BOPD has been restored in a well previously closed due to proppant production with limited impact on well productivity. A post-job monitoring program has been designed to further evaluate this technology.

The development of enzymatic calcium carbonate scale consolidation has led to a method for chemical consolidation of proppant fractures that is more environmentally friendly than alternative methods, is reversible and has limited impact on well productivity.

Introduction

The Gorm field is a chalk reservoir located in the Danish Offshore sector, created by salt uplift (Nederveen and Damm 1993). It produces from the Danian and Maastrichtian formations via approximately 30 active mainly horizontal production wells. The oil producers are generally completed using the Perforate, Stimulate, Isolate (PSI) concept (Damgaard et al. 1992). Pressure support is provided by four vertical and seven horizontal basal water injectors.

The reservoir is tight, with matrix permeability of around 1 mD. The wells are either stimulated by means of matrix acidisation, high rate acid fracturing or sand propped fractures. Proppant and sand are used interchangeably throughout this paper, with both terms referring to the sand based proppant used during stimulation.

Three key challenges to production are; scale formation (both barium sulfate and calcium carbonate),pressure maintenance due to irregular waterflood patterns and water short cuts, andsand production from de-stabilised fractures.