Optimal Practices To Remediate and Control Fines Migration in Inland-Water Wells in the Maracaibo Basin, West Venezuela

This paper summarizes the following aspects of a comprehensive program intended to develop optimal practices for the stimulation of wells in the Ceuta field, a developing area located in Lake Maracaibo, West Venezuela: lab testing to diagnose formation damage mechanisms and to qualify proposed treatments; operational practices including injection sequence, treating volumes for optimal radial penetration and diversion techniques for uniform placement; recommended safety and environmental practices. Also, detailed examples of treatments performed in six inland-water wells in the Ceuta, Area 8 South Central area within this field are provided. The average production rate for these wells before the implementation of these practices was 419 BOPD. The implementation of the guidelines provided in this paper resulted in an average post-production rate of 2100 BOPD with a twelve-month average decline rate of 1.6 BOPD. The enhanced methodology has been implemented with success in other fields in the Maracaibo Lake area known as CentroLago, Lagotreco and Lagocinco. Results from treatments in these areas are also summarized and discussed. Introduction The Ceuta Field is a developing oilfield located in the Maracaibo Lake area, West Venezuela (see Figure 1). Hydrocarbons of ca. 20–37 º API are produced in this field from sandstone layers with permeabilities ranging between 25–115 mD in a gross interval of approximately 700 feet that includes the reservoir units commonly referred to in the Maracaibo Basin as units Misoa B 3.4 to B 6.0. Bottomhole temperatures range between 290–310 ºF and reservoir pressures range between 4000–6500 psi with depths of about 16,500 ft. The stimulation of wells in this field is a challenging task from technical and operational standpoints due to the diversity of formation damage mechanisms (chiefly fines migration, with deposition of clays, organic compounds and scales also occurring), bottomhole temperatures and large pressure gradients between producing sandstone layers. The purpose of this paper is to report recent innovations in the matrix stimulation strategy for the Ceuta field that have resulted in improved production results over previously reported stimulation protocols. Specifics regarding typical fluid formulations, operational practices for injection sequence, treating volumes for optimal radial penetration, diversion techniques for uniform placement and recommended safety and environmental practices are described and discussed. The recommended stimulation protocol, with is referred within PDVSA as "Liquid HF", has been successfully implemented in other fields in the Maracaibo Lake area Centro Sur Lago, Lagotreco and Lagocinco. Results from stimulation jobs in these fields with the Liquid HF protocol are also summarized and briefly reviewed. Near-wellbore Damage Mechanisms Laboratory studies performed on crude oil and core samples from the areas of interest allow determining the prevailing mechanisms that impair well production. A previous study 1 determined that fines migration is a key impairing near-wellbore area for the Ceuta field. This assessment was achieved via mineralogical analyses by means of X-ray diffraction, flow tests on representative cores from the field and scanning electron microscopy. These studies concluded that there are clay particles, specifically kaolinite and smectite/illite ("mixed layer"), that can be dispersed with relative ease and migrate with fluid flow to further deposit in the pore throats, thus reducing the effective permeability of the porous media.