Importance of Well Monitoring to Generate Correct Diagnostics and to Solve Formation Damage Problems - Case Studies
Authors: Perin Vujin Slavica 
Published: February 2016

Abstract
In highly unconsolidated formations, the production of formation fluids is associated with the production of formation sand. Sand production leads to reduced productivity and excessive maintenance to both downhole and surface equipment in most cases. Mostly applied sand control method in Serbia is gravel pack, and almost third of total oil production comes from wells with gravel pack.
Sand control management, monitoring and well maintenance are essential to achieve planned oil production and to decrease operational costs.
Presence of clays in sandy collectors leads to poor gravel pack performance. Formation damage due to the clay swelling and defloculation causes restriction of fluids flow to the wellbore, and consequent production decrease. Besides clays, organic and inorganic deposits influence formation damage causing further fluid production decrease through the well production life circle.
This paper presents two case studies that deal with different aspects of formation damage and solution of the problems in wells completed with gravel pack. The importance of well monitoring to generate correct diagnostics has been discussed.

Introduction
The pore space of the near-wellbore zone is a part of the collector rock most exposed to different influence, from the moment when the bit enters the reservoir during the drilling of the well until the liquidation of the well, or in other words during the entire life of the well.
The formation damaging may occur during:Drilling operationsCompletion operationsStimulation operationsWork-over and kill jobsProduction operations
During each phase of the well operations there occurs to a greater or lesser degree the damage of the pore space of the near-wellbore zone which is reflected in the reduction of its permeability. Minimal damage of the near-wellbore zone is at the same time an important precondition for achieving maximum productivity of the well. The permeability of the damaged zone is lower than the natural permeability of the collector rock. Establishment of natural permeability of the damaged near-wellbore zone can be achieved by different activities, but this leads to the waste of both time and money. Therefore, prevention represents the first step in the protection against damage.
This paper deals with the monitoring and rehabilitation of the near-wellbore zone damages inflicted during the years-long oil production. Two wells have been chosen for the analysis: K-84and V-101.

Case Study #1

The Problem
The K-84 well produces through the 1141.00–1139.00 m interval from one of the reservoirs which is a part of a complex of reservoirs that vertically spread one above the other. The collector rock is sand and sandstone with intermediary levels of clay and high contents of silt-clay components. A gravel pack was installed with the quartz sand of 0.8–1.6 mm granulation to stabilise the near-wellbore zone. This granulation of the sand was chosen to enable the production of silt-clay components, the fines, from the reservoir sand so that there would be no plugging and reduction of the permeability of the gravel pack. As the reservoir energy was insufficient for the natural flow, the artificial lift method has been applied. A sucker rod pump (SRP) was installed.