Development of Early Water Breakthrough and Effectiveness of Water Shut off Treatments in Layered and Heterogeneous Reservoirs

Abstract

Progressive percentage of total fluid produced in the oil industry is formation brine. Ever, increasing water cut will reduce oil recovery, diminish wells' productivity and increase cost of eventual artificial lift and produced water handling. This paper investigated the problem of early water development in layered and heterogeneous reservoirs and determined the effect of different reservoir parameters on the development of water front movement in the presence of what is considered as a thief zone. A water injection in a line-staggered pattern was simulated to analyze the effect of various reservoir parameters on the water breakthrough time, WBTT, and the evolution of water front in the thief zone as well as other reservoir layers. Sensitivity analysis was conducted to investigate and determine the effect of most reservoir parameters that would cause and aggravate irregular advancement of injected water resulting in early water breakthrough and high water cut wells. These reservoir parameters included layers' horizontal permeability, Kv/Kh ratio, and thickness of high permeability layers. Threshold of these parameters beyond which its effect would be constant was determined to help operators to predict the possibility of early water breakthrough through thief zones for better waterflood performance and hence better decision making process. From the first part of the study, a range of extreme cases was then selected to test the effectiveness of the currently available water shut off, WSO, methods of Cement squeeze, polymer-gel, as well as mechanical isolation. This paper simulated these WSO treatments to investigate its effectiveness in delaying the water breakthrough time, reducing high water cuts, and reducing the water handling problem. The paper summarizes the applicability of these WSO treatment methods and the condition under which they are effective and when they are not so. 1. Introduction Excessive amount of water with produced crude oil has been a continuing problem in conventional petroleum production technology worldwide. In recent years, over 1200 million barrels of produced fluid were water compared to only 200 million barrels of oil and condensate in addition to 200 million barrel oil equivalent, BOE, of gas produced. On average, 75% of total fluid produced worldwide is formation brine.1 The fast progressing percentage of water production will inevitably lead to hampering wells' productivity. Moreover, progressive water cut will also terminate recovery process leaving considerable amount of oil in place. For instance, the resulting by-passed oil in mature reservoirs may range from 40% up to 90% of the oil in place, depending on fluid properties and thickness of the pay zone. In the Arabian Gulf region, most petroleum reserves are located in carbonate reservoirs which are characterized by complex textures resulting from various diagenesis processes. These results in non-uniform fluid flow in the reservoir with water advancing in high permeability streaks causing early breakthrough.2 With decreasing oil rate replaced by increasing water rate, the cost of water lifting, handling and disposal will cause early shut-downs of wells thus making the reservoir development projects uneconomical at low value of recovery factors. Water production is one of the major technical, environmental, and economical problems associated with oil and gas production. Water production can limit the productive life of the oil and gas wells and can cause several problems including corrosion of tubular, fines migration, and hydrostatic loading.3 It may be caused due to several factors, such as bad well completion design, drilling a well deep into the oil water contact, which would cause the production of more water than oil in the long run, or simply due to waterflooding, which is a vital mechanism used to maintain the reservoir pressure while producing, and helps to increase the oil recovery by a significant margin.

Application of Hydrogels and Hydrocarbon-Based Gels in Oil Production Processes and Well Drilling

“…In addition, the depth of penetration is not taken into account explicitly, which prevents the description of the process of the subsequent recovery of the watercut. However, it is possible to use the results of analytical calculations in commercial hydrodynamic simulators (Black Oil) to predict not only the starting indicators, but also the dynamics of operating indicators during the time of the effect [183][184][185][186][187].…”