Increasing well production without compromising reservoir management and well integrity in an environmentally friendly manner is a common objective within the producing companies. This philosophy has led to the development and introduction of many innovative technologies and strategies into the oil and gas industries.

The need to improve brown field productivity has given birth to many innovative technologies such as short-medium radius drilling, 4D seismic, water and fines control, artificial lifting, pressure maintenance and deep penetrating damage removal acid system.

Minimising fines migration and improving high water cut well productivities via improved treatment fluid designs, detailed candidate selection, along with enhanced pumping methods are some of the many innovations that have yielded positive results in aged field production enhancement.

Before 1996, Mud acid was the common Hydrofluoric acid (HF) system for damage removal in Niger Delta at large. Retarded acids like fluoboric acid were introduced and applied with mixed results. Also, high water cut stimulation was limited to only 30% water cut while wells with higher water cut could not benefit from production increase via acidising. Common diverters such as water seeking polymer, foam pad and benzoic acid, ball sealers, packers and gel acid have been applied for water control during HF treatment. However, no particular diversion method had shown consistent results in the Niger Delta reservoir with Darcy permeability. Additives selections were sometime generic and in many cases there was no specific focus to the common enemies of effective well production "fines migration".

In 1996, the first Hydrogen delayed retarded HF acid was successfully pumped in Shell Petroleum Development Company Nigeria (SPDC) wells. Nicholas et al, 2001, published the performance of this system in SPE paper no 56527. After this success, the drive and confidence to stimulate high water cut increased. The solution to high water cut wells productivity enhancement was accomplished in 2001 through detailed candidate selection, recipes design and pumping method1 .

The need to reduce the cost of the retarded HF acid introduced in 1996 and also improve acidising performance especially in high water cut wells, fines dominated zones and heavy crude led to more critical look at design philosophy, recipe selection, pumping procedures and consideration to trial similar Hydrogen delay retarded HF acid system (SRH-RHF) in 2005. The second Hydrogen delay retarded HF acid system (SRH-RHF) is supplied by another contractor. SRH-RHF was applied in heavy crude with fines problems and the results of the trial were remarkable. Success rate has been greater than or equal to 300% over conventional mud acid performance on similar wells and average payback time has been less than twenty days with quantifiable reduction in damage skin or increased productivity index.

This paper reviews the acidising history of Hydrogen delayed retarded HF acid system (SRH-RHF), details the approach to candidate selection, case specific recipe design for high water cut wells, mechanism of fines/clay migration and control methodology, along with one of the successful approaches to acidise heavy or medium crude. Laboratory quality control also forms part of this paper.

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