ABSTRACT

Of critical importance in the proper application of inhibitors within oil producing wells is the delivery of the chemical throughout the system. In traditional batch treatment, an excess of chemical is required to ensure a sufficient quantity of corrosion inhibitor is applied to all metal surfaces. The performance of the chemical and retreatment interval are based upon film persistency. The results of two field trials using a novel batch treatment using slow release (mass transfer controlled) solid corrosion inhibitors is presented. Using an encapsulated batch treatment, the chemical performance and retreatment interval are based upon inhibitor concentration in the system. The total chemical usage decreases and the treatment interval increases twelve-fold.

INTRODUCTION

During the production of oil and gas, water (or brine) is typically produced as an undesirable byproduct. When brine is produced in the presence of carbon dioxide, carbonic acid species may occur in solution resulting corrosion or metal loss from metal goods utilized for production. As the well ages, the pressure in the reservoir slowly drops resulting in greater water production and increased corrosion failures. 1'2 In order to prevent failures due to metal loss, corrosion inhibiting chemical are frequently introduced into the producing wells. 3

There are several methods for applying corrosion inhibiting chemicals to protect metal goods. The corrosion inhibitor may be supplied as a free flowing liquid, a water external emulsion, an oil external emulsion, or solid state. The inhibiting chemical may either be applied intermittently (batch) or continuously into the producing well. In continuous application a liquid inhibitor is pumped either down the backside of a well or through capillary tubing to the bottom of a producing well. Solid and emulsion based products are not generally applied continuously though due to their physical properties their chemical return profile may simulate continuous injection. 4 Batch applications include applying the corrosion inhibitor down the annulus followed by a liquid flush, applying the inhibitor down the producing tubing and shutting the well until the fluid applied chemical reached the bottom of the well, displacing all the fluid from the production tubing, or squeezing the chemical into the formation.

In batch and flush applications, the key is to deliver the chemical to the proper location at the proper time to provide protection from corrosion and metal loss. When using a standard liquid based corrosion inhibitor applied into the annulus, the flush is designed to displace the fluid column and result in the immediate delivery of the chemical inhibitor up the production tubing. As the batch of chemical inhibitor is produced through the tubing, a corrosion inhibiting film is formed on the metal surface of the well. As the well continues to produce, the inhibitor films are lost and another batch treatment will be required. Typically the time between batch treatments ranges from 3 days to 1 month depending upon both well production conditions and properties of corrosion inhibitors. The volume of chemical treated is based upon the total metal surface treated and the corrosivity of the system. A batch treatment generally uses more chemical than would be required to treat the produced liquids on a continuous basis.

One method to gain the benefits of continuous injection is to supply the chemical inhibitor into the annulus via a batch producing. However instead of immediately producing the inhibitor, the treatment is designed such that a reservoir of chemical remains in the well to slowly release corrosion inhibitor. The transport of emulsions based upon this princ

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