Design Of High-Density Fluid Gravel Pack for Assa North Lower Completions
Authors: Oyeintonbra I. , Adeyeba A. , Moses U. , Emmanuel O. , Yahaya I. , Imoyo O. , Joseph M. , Raymond L. 
Published: February 2025

With Nigeria's gas demand projected to reach 22.5 Bscf/d by 2030, the ANOH project emerged as a significant gas condensate development endeavor in the country. This project aims to meet the increasing domestic demand, which is expected to constitute 60% of the total demand by 2030, compared to 30% in 2020. To support Nigeria's National Gas Master Plan and Shell Petroleum Development Company’s (SPDC) gas obligation, the ANOH project involves the drilling of six wells in phase 1, targeting a total of 4.3Tscf of gas and 197 MMstb of condensate in support of the federal government of Nigeria’s National Gas Master Plan and fulfill part of the SPDC’s gas obligation.

The reservoir's characteristics, include shallow depth, reactive shales, and unconsolidated formations, necessitated effective sand control measures during completion operations. The reservoir is also over-pressured with an estimated gradient &gt;0.67 psi/ft and a very high permeability (&gt;5D). The objectives of the lower completion include engineering a water-based drill-in fluid (DIF) to ensure wellbore stability, minimize formation damage, optimize gravel placement around the screen due to high deviations and permeability at the reservoir depths, and design a single-trip gravel pack and treatment system. A non-polymeric viscoelastic surfactant was selected for its proppant suspension capabilities and compatibility with a filter cake breaker. Due to the high reservoir pore pressure, a high-density brine (14.0 ppg CaBr2) was chosen, requiring careful consideration of its hazardous nature. Also, a suitable filter cake breaker fluid consisting of zinc bromide was selected to ensure the wells would flow naturally after the formation isolation valve (FIV) was opened.

Extensive testing, including rheology, return permeability test, fluid loss, compatibility testing with formations water, filtrate and WBM filter cake, and corrosion assessments, was conducted to validate the WBM formulation and gravel pack deployment tool selection. A Gravel Pack Service Tool with post gravel pack fluid pumping capabilities in conjunction with alternate pack screen system and FIV was selected, while specific quality assurance measures were implemented to ensure successful job execution.

The completion process for one of the ANOH wells involved deploying the lower completions assembly to target depth, achieving &gt;100% gravel placement in the open hole using alternate path screens along with a Viscoelastic surfactant as the carrier fluid, successfully inflow testing the FIV and deploying the 7-in. tubing with its completion accessories. The well was displaced to underbalanced fluid (inhibited water) after landing the tubing hanger to aid cycling of the FIV during the well clean up. The wells' production rates exceeded predictions with minimal drawdown and low skin value demonstrating the effectiveness of the implemented completion strategy.

This paper provides a comprehensive overview of the fluid design, equipment selection, and execution process for completing the ANOH wells, contributing to the successful development of this crucial gas and condensate project in Nigeria.