No abstract

Matrix acidizing is commonly used to enhance the production of damaged wells. As to undamaged wells, it is commonly believed that matrix acidizing can hardly enhance their productivity or injectivity. In Iraq X Oilfield, the acidizing operations for four undamaged wells have failed to enhance their performances, which seemed to meet this assupmtion. A novel deep penetrating long wormhole creation acidizing technique has been proposed and tested in X Oilfield to stimulate these undamaged wells. In comparison with averaged acidizing technique, it can create a much deeper dominant wormhole by applying a much larger acid volume and pumping rate so as to further enhance the well's productivity or injectivity. Very important, it applies a new type of solvent that can better remove asphalt from the rock surface to facilitate the rock-acid reaction and a retarded acid system to make sure the acid can go deeper into the formation. This novel technique has been tested in all of the fore-mentioned three production wells and one injection well, which have been failed by averaged acidizing technique before. For these three production wells, the production enhancement ratio after using averaged acidizing technique was only 7% on average. However, the well test result for one of these wells showed that despite the low production enhancement, the post stimulation skin factor is −2.08, which showed that the near wellbore pollution had already been removed by the average acidizing technique. Then they were treated with deep penetrating acidizing technique and the production increased correspondingly. In addition, for the injection well, after averaged acidizing technique treatment, the injectivity index quickly decreased from 252m3/(d.Mpa) to 95m3/(d.Mpa) in only two months. However, after the deep penetrating technique operation, the injection pressure stabilizes at 0 injection pressure for more than 9 months with the same injection rate. This new technique has been the first time tried in this porous limestone formation to stimulate undamaged wells after the failure using averaged acidizing technique. Though first tried in this Iraqi Oilfield, it can be extraopolated to other oilfields with similar limestone formation around the world.

CNOOC Iraq Limited operates three oil fields in Missan Province in Iraq. They are all large onshore oilfields located 350 kilometers southeast of Baghdad. In order to support reservoir pressure, plans are underway to implement a water injection scheme. The injection water comes from three different sources; produced water, aquifer water as well as river / agricultural water. Considering the nature and varying chemistry of the source water, particular attention had to be given to selecting the material for the water injection wells. This paper describes the approach adopted in selecting the materials for Missan fields’ water injection system.

CNOOC Iraq Limited (CILB) operates the Missan oilfield in Iraq, which consists of three oilfields: Buzurgan oilfield, Abu Gharib oilfield and Fauqi oilfield. To maximize production from the field it has been necessary to overcome different challenges related to asphaltenes (tubing deposition, formation damage, emulsions) – firstly by properly understanding the fluid behaviour, and then by developing and implementing mitigation strategies. To understand the asphaltene stability of the reservoir fluids, an isothermal depressurization study was performed on a monophasic bottomhole sample from the reservoir’s main production unit. Asphaltene Onset Pressures (AOPs) were identified and used for tuning an equation-of-state model to generate an asphaltene precipitation envelope (APE). Modelling software was used to calculate pressure-temperature profile of fluids both in the near wellbore region and production wells and determine if they entered the APE. This was reviewed against historical field data to assess if asphaltene issues were predictable. Common fluid property screening tests (e.g. De Boer plots, Colloidal Instability Index) under-predicted the occurrence of asphaltene precipitation in the oilfields. When fluid pressures and temperatures in the reservoir and well environment were compared against the modelled APE, they showed the reservoir fluids passing through the asphaltene instability region for most wells, indicating a risk of deposition in the tubing and in the formation. Comparing predictions with field data highlighted that precipitation of asphaltenes does not always result in tubing deposition and additional factors such as watercut and oil viscosity need to be considered. Other fluid-related issues, such as stable emulsions and formation damage, have been observed in the field and require managing. Results from this study show that these can be explained in terms of asphaltene stability issues arising from fluid P/T behavior and interactions with water. The importance of drawdown management, already practiced by the field operator, is shown to be a key tool for managing and controlling asphaltene issues. The value of optimizing solvent-based stimulations and retaining the ability to stimulate ESP-lifted wells is also demonstrated. Measuring asphaltene stability using virgin reservoir samples, and applying fluid screening tests, are common activities during new field appraisals. The results inform high value decisions, ranging from completion design to reservoir management strategy. This study, conducted on a mature field with known production history, shows how results from fluid characterisation studies relate to actual experience of asphaltenes during production. The use of fluid studies in diagnosis and treatment of operational challenges is also demonstrated.