Perforations-A Prime Source of Well Performance Problems
Authors: Suman George O. 
Published: December 2007

As sure as technology comes up with a nifty solution to a persistent problem you can bet it will have to come up with equally nifty solutions problem you can bet it will have to come up with equally nifty solutions to the new problems caused by he original solution. This is called progress. progress.

Introduction

This investigation was undertaken to determine the cause of difficulties encountered in injecting fluids through perforations into unconsolidated permeable Pliocene and Miocene sand reservoirs. The particular Pliocene and Miocene sand reservoirs. The particular wells in question are in the South Pass Block 24 and Block 27 fields, located at the mouth of the Mississippi River. We felt that injectivity impairment, by preventing proper placement of sand-control, was a primary cause of the high incidence of sand-control primary cause of the high incidence of sand-control failure and associated casing damage. We expected that by understanding the source of injectivity impairment we could also obtain a better insight into the cause of productivity impairment common to those wells.

Impairment of injectivity into unconsolidated sands can be a serious problem since a essential part of the completion is the injection of sand-consolidating fluids into the formation through the perforations, or the deposition of gravel in the perforation tunnels (the holes through the casing and cement sheath). Portions of an interval not accepting consolidating Portions of an interval not accepting consolidating chemicals would be subject to early sand-control failure. Treatment through impaired perforations could cause the impairment to become "locked in place" by the treatment plastics and result in seriously decreased well productivity. In gravel packing, the perforation tunnels must be filled with properly sized perforation tunnels must be filled with properly sized gravel to prevent the tunnels from becoming filled with fine formation sand when the well is put on production. Perforation tunnels filled with fine production. Perforation tunnels filled with fine formation sand severely restrict fluid flow. The tunnels can most likely be filled with gravel only if fluid can flow out of the wellbore through the perforation tunnels and carry gravel into them during perforation tunnels and carry gravel into them during gravel-packing operations.

Perforation Flow Impairment Perforation Flow Impairment There has been widespread evidence of a severe perforation flow impairment problem in Shell's perforation flow impairment problem in Shell's Delta Div. in South Louisiana. Plastic consolidation fluids usually could not be pumped outward through the perforations without acid stimulation or fracturing, neither of which has assured uniform placement throughout the perforated interval. Gravel-packed wells have commonly required acidizing before full-depth-allowable production could be obtained. Recovered gravel-pack production could be obtained. Recovered gravel-pack screens and blast joints have frequently shown only one or two eroded holes (Fig. 1), suggesting that most of the produced fluid was coming from only a few of the perforations. Steps were taken, therefore, to isolate the cause of impairment of well injectivity and productivity. A process of elimination was begun in the field concurrently with laboratory investigations. The extent of perforation impairment and its relative importance with perforation impairment and its relative importance with respect to other possible sources of trouble (drilling mud or cement or completion fluid) were studied individually.

Drilling mud and cement were considered to be possible contributors to impairment primarily because possible contributors to impairment primarily because of the way dispersant-type filtrates affect the clay material in the formation.

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