Abstract

Wells requiring combined sand clean out and acidizing operations have been routinely treated using BHA's containing different nozzles in multiple trip operations. This is especially true for sanded-up completions. The normal scenario would be to use a standard wash nozzle for both acidizing / sand cleanout operations or to use a switchable nozzle for the sand clean-out, POOHpooh and then run a rotating jetting nozzle (for acidizing). However, the former scenario would not be optimal because standard washing nozzles are not effective against filter cakes / scale and the latter alternative might be in some situations an over-kill leading to really expensive operations.

This paper describes the use of a specialized nozzle that generates a ‘vortex’ or a fast swirling mass of fluid in the completion tubulars / open hole. Jet velocities and rotational speeds commonly exceed 460 ft/sec and 8000 rpm, respectively. Because of a specially designed internal flow guide, this nozzle entrains debris and also provides improved jet coherence and projection compared to standard jetting nozzles. This dual feature of the nozzle made it particularly attractive for use in combined sand clean out / acidizing operations of sanded up injectors. This nozzle also has no moving parts or rubber seals, seals; therefore, the commingling fluid phases no sidewould not aeffects result to the efficiency of the tool as a result of commingling fluid phases.

These injectors are vertical completions with architecture ranging from perforated intervals to standalone screens. The sediments consist of a mixture of organic deposition, fine siliceous material and carbonate scales. This paper analyzes the improved post injectivity and compares results using this nozzle to those using a wash nozzle / rotating nozzle combination on the basis of cost, operational efficiency / simplicity and technical effectiveness. These results suggest that some non - aggressive scales can also be treated using this nozzle as an alternative to a rotating jetting system leading to reduction in well intervention cost through a single trip approach.

Introduction and Justification

Operators within the Nigerdelta as a standard have sand control measures in place. This may vary from basic standalone screens, slotted liners, pre-packed screens or standard gravel packs with wire-wrapped screens. The problem of unwanted sand production and establishing the most effective and economical means of removal during remedial treatments is a re-occurring challenge [1].

The removal of sludge and solid fill like sand, proppants, drilling, proppants, drilling solids or lost circulation materials can be circulated out of wells using a variety of techniques. Key factors governing the approach for effective removal such as completion geometry, reservoir pressure, temperature, particle size and density, etc. have been studied extensively over the years and can now be properly simulated and engineered [2].

Clean-outs within near vertical wellbores are often viewed as simple, yet best practices offer several possibilities to improve efficiency of exercise and thus save cost. The use of coiled tubing with the appropriate tools and carrier fluids that have efficient lift properties and yet low friction pressure can be a major advantage but expensive in some cases. A unique tool can improve on this process eliminating the need for complex carrier fluids, and at the same time act as an effective diversion tool for stimulation treatments.

In the injector wells treated the general objective was to wash and dissolve the sediment plug across the zones of interest, clean the sandface face completion and stimulate the near wellbore region with aa unique emulsified acid system. This acid system removed the wellbore impairment caused by scale deposition/fines migration. The acid was placed by a specialized nozzle offering effective penetration of the treatment fluid via the vigorous action of high speed fluid swirl through the tool. This unique feature was successful in both fill removal and stimulation with minimum effects to the completion hardware and massive post treatment gains.

The fact that the same wells were previously treated with different clean-out and stimulation techniques, we are able to closely compare the different methods and proffer the most economic, suitable and successful technique for future scenarios.

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