Abstract

A major challenge identified by ADMA OPCO is the time delay and subsequent lost production between a well being completed with the drilling rig until it is acid stimulated using a multi purpose barge and put on production.

Some wells in ADMA OPCO fields that are perforated using conventional perforating techniques will not produce until stimulated with acid. A new perforating technique has been deployed that creates clean, low skin perforations and allows the well to be produced at commercial rates while waiting for the multipurpose barge and in some cases eliminate the need for stimulation.

This new perforating technique utilizes a unique job design process and specific equipment to ensure the guns are detonated in the correct environment to create a dynamic underbalance immediately after perforating. Laboratory tests show how this fast acting dynamic underbalance created across the perforated interval is used to clean perforation tunnels and produce low to zero damage perforation tunnels1–2.

This paper describes how this new perforating technique was used in two ADMA OPCO wells to wireline perforate in multiple runs a carbonate reservoir which then produced more than 2500 bbl/day oil before acid stimulation. A fast acting memory recorder was run with the guns to record pressure transients in the well bore at the time of perforating. The subsequent acid matrix job on these wells further improved productivity.

This paper will show the perforating strategy, execution requirements, post job monitoring and the final results. This is the first fully documented case of this perforating technique being used in a carbonate reservoir and the first time this technique has been used in Abu Dhabi.

Background

ADMA OPCO producing wells, which are located offshore, are matrix stimulated with acid prior to production. The matrix acid stimulation is carried out using a barge outfitted for this purpose. Due to the barge logistics and the drilling program some wells have to wait some time after drilling is completed (months in some cases) before they are acid stimulated and brought on line.

ADMA OPCO are constantly looking for ways to improve efficiency and well productivity. They reviewed how these wells are completed and perforated to see if any improvements are possible. ADMA OPCO completion requirements Fig.1 for the producing wells often require 2 inch carrier perforating guns to be run through tubing and shot in 7 inch casing in a static underbalance environment around 1000 psi. In many cases after perforating with this method the wells were not able to flow into the production line with a back pressure of more than 1000 psig until they had been acid stimulated.

These wells often require several runs of perforating on wireline to complete. Using the equations for underbalance determination3 the optimal static underbalance to clean up perforations in these reservoir conditions is ∼7000 psi. The reservoir pressure in these cases is well below this optimal pressure so meeting this requirement is impossible. Also executing a job with such a high drawdown in these conditions would be dangerous and is not feasible from an operations standpoint. Also after the first run shot with a static underbalance the well will be at balance conditions so any subsequent perforating runs will be made at balance and not benefit from an underbalance surge for clean-up.

The well log data was evaluated to determine optimal perforating intervals and the applicability of the dynamic underbalance perforating technique to these reservoirs. For well number 2 the reservoir being perforated is oil filled Dolomite with 15 to 25% porosity, as seen in the petrophysical interpretation, Fig. 2. The micro electric imaging data from the FMI (Formation Micro Imager - FMI) was used to establish the location of fractures and a permeability profile, Fig 3. The pressure and mobility results from the wireline test tool (Modular Dynamics Tester - MDT) were also a key part of the analysis, Fig. 4. Well number 1 has very similar characteristics.

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