Oil production from some of wells in the White Tiger field producing from a fissured Basement reservoir; have been impaired by excessive water production. Excess water not only reduced the artificial lift efficiency, but also imposed various damages to the oil zones. Since 2002, a joint industrial project was set up to study the feasibility of performing water shutoff treatments in the open-hole completion oil wells. The study involved evaluation of a high temperature polymer base water shut-off fluid for deep penetration of the fissure formation and a micro-fine cement system for sealing off the water entries. Based on this study, a cost-effective chemical treatment method was progressively developed. In 2005, the treatments were performed through-tubing with and without isolation packers. Two Candidate wells were having 6.5" open-hole size, at approximately 4,200 meter TD, and 150 deg C reservoir temperature. The water cut were 95% in one well and 30% in the other well. It was found that these two wells certainly had big difference in fluid injectivity, and original designed treatment was modified on site. This paper summarizes key lessons learnt including tool and packer conveyance, mixing and pumping of water shut-off fluids under offshore rig and wellsite conditions. It also shares a method of post treatment production evaluation and suggests operational change to improve the production. Introduction White Tiger Field in offshore Vietnam is producing from a highly fissured granite Basement formation. Basement consists of igneous crystalline rocks characterized by petrography heterogeneity because they were formed in different tectonic activities in their geological evolution. Since being formed to recent, the basement rocks of the Cuulong basin have been strongly affected by different alteration processes. These processes changed not only the composition, petrophysical characteristics, but also were principal causes creating good reservoir properties of some granitoid basement bodies. Some main alteration processes are volume shrinkage due to the crystallization of magma lavas, alteration due to the tectonic activities, alteration due to the hydrothermal activities, alteration due to the weathering activities. The inside volume of magma bodies is often shrank when the magma lavas crystallized and solidified. This volume shrinkage caused by sudden change of temperature as well as by viscosity increase during the times that these magma lavas crystallized and resulting in the formation of individual micro fractures and misco-vugs in granitoid rocks. These micro-pore types can be only beneficial for reservoir if they had linked together by fractures and microfractures, which were formed due to tectonic activities at later times. The tectonic activities are principally factors making strong and widespread alteration of basement rocks. The basement rocks have been fractured, broken and catalazited at various degrees, developing different fracturing systems with different directions. The fracturing and breaking did not change the rock composition, but they strongly altered the structure, texture and particularly the petrophysical characteristics of the basement rocks. The petrophysics characteristics of altered basement rocks in the White Tiger (Bach Ho) field change very strongly both with depth and area. Permeability ranges from less than 1mD to hundreds mD. Two principal porosity types that are fractured/micro-fractured and cavernous/micro-cavernous pores can always be observed in the altered granitoid rocks (figure 1).
This paper presents the results of propped fracturing operations conducted in the past 12 years in the Bach Ho (White Tiger) field offshore Vietnam. High temperatures (>275oF) and closure stress (>8,000 psi) combined with the fact that fracturing has to be performed from a vessel make the execution of fracturing treatments operationally difficult and challenging. More than 60 treatments have been performed in over 40 wells placing over 3 million lbm of proppant with a success rate greater than 85%. The wells targeted were both injector and producer wells. The post treatment results have been excellent with an average increase in Productivity Index (PI) of greater than 5 times. This study discusses the properties of the various hydrocarbon-producing zones in the Bach Ho field. A general discussion of reservoir properties and damage mechanisms is included, which demonstrates the potential for stimulation and the associated benefits. The methodology adopted in the design, execution and evaluation of the fracturing treatments is discussed. Discussion on the rig-up of the fracturing vessel and the necessary modifications for efficient operation is also included. A review of the treatments indicates that the majority of them are conducted at a flow-rate of 20–25 bbl/min (bpm), with a maximum proppant concentration in the range of 8–10 ppa (lbm of proppant added to 1 gal. of clean fluid) and proppant quantities of 60,000 to 80,000 lbm per treatment. High leak-off limits higher proppant concentrations and volumes. Higher rates are desirable but are limited due to limitation of equipment on the fracturing vessel. Zones targeted are both the Oligocene (sandstone) and the naturally fractured Basement. Propped fracturing has been found to be very successful in the Oligocene whereas different types of treatments like propped fracturing, acid fracturing and acidizing have been tried in the Basement with limited success. Finally the lessons learned and the experiences gained in this field are shared. Introduction The Bach Ho field is located in the South China Sea, 120 kms south-east of the port of Vung-Tau in Vietnam. The field was originally discovered in 1974 but was placed in production only in 1986. Production is from the Miocene, Oligocene and the Basement formations flowing into a Floating Production Storage Offshore (FPSO) loading vessel. Average seawater depth is 165 ft. There are 215 wells in the White Tiger field which are mostly directionally drilled up to 70 degrees angle. There are also 3 horizontal wells. The oil-bearing horizons in the White Tiger field are found in 3 main reservoirs: The primary target is the fractured granite basement which is typically oil saturated with a gas cap. The secondary target is the lower Miocene and Oligocene, which are interbedded sandstones saturated with oil. Some of the wells show initial production as high as 10,000 bopd. The drilling practices and other damage mechanisms discussed in the next section restrict most of the wells from producing to their potential from reservoir engineering considerations. Hydraulic fracturing has been found to be the most effective technique to bypass skin-damage in the near-well bore region and create a high conductivity conduit for production enhancement. Fracturing was started in the Bach-Ho field as early as 19941. Target zone for fracturing has mostly been the Oligocene as it has reasonable recoverable reserves, does not have water zones nearby like the Miocene and is not naturally fractured like the basement. Some treatments have also been targeted in the basement but with limited success due to very high leak-off. This paper discusses the design, execution and evaluation cycle of the project along with the problems encountered in the execution and the lessons learned.
The first hydraulic fracturing of wells in Vietnam were successfully performed Offshore in the Bach Ho (White Tiger) Oil Field. Near-tip-screenouts rather than tip-screenout treatments were performed. The goal of the project was to improve production from existing wells rather than drill new wells and reduce the cost per barrel produced. This case study involves wells with multiple perforated zones completed in the Oligocene sandstone. Zones were selectively fractured in order to optimize production. A detailed description candidate selection, design, execution and evaluation processes are presented. The Bach Ho field has been producing for 8 years but not at its potential due to various reasons including drilling and completion fluid damage. Although acidizing was an option for damage removal, hydraulic fracturing was selected as a way to bypass near-wellbore damage and generate a negative skin. Production simulators were used to quantify postfrac production. Due to suspected high closure stress, high strength proppant was selected and ramped in a high temperature fracturing fluid. Calibration treatments were conducted on several wells to quantify fluid leak- off, fracture height and Young's modulus. Based on the results of the calibration treatment, fracture designs were modified. As predicted by computer simulation, near-tip-screenouts occurred as planned. The treatments were performed using a work boat with skid pumping/blending equipment, a computer monitoring/operation center and a laboratory. Strict QC procedures were followed to ensure the quality of all products. Postfrac well tests results and production data are presented. Overall, the fracturing campaign was very successful with wells showing negative skins and up to a five fold increase of production in agreement with systems analysis predictions. Introduction Tip-screenout fracturing techniques are routinely applied in soft formations where creation of fracture width is not a major problem. A modified technique termed "near-tip-screenout" was recently applied in the Bach Ho field, Offshore Vietnam resulting in improved oil production. This technique requires bridging of the proppant toward the tip of the fracture rather than at the tip to obtain adequate fracture conductivity. The Bach Ho field is located approximately 140 km from the port of Vung Tau in Southeast, Vietnam. The field was originally discovered in 1974 but not placed on production until 1986. Production is form the Miocene, Oligocene and basement formations flowing into a Floating Production Storage Offshore loading vessel. Present production is approximately 130,000 BOPD. Stimulation was considered as a technique for production enhancement to exploit the full potential of the field. The Oligocene formation was targeted for potential stimulation because it offered the greatest potential for reserves, did not have water nearby as in the Miocene and was not highly fractured like the basement. Near-tip-screenout fracturing was applied in the Oligocene formation, a deep, hot sandstone located immediately above the basement (granite). P. 285
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractOil production from some of wells in the White Tiger field producing from a fissured Basement reservoir; have been impaired by excessive water production. Excess water not only reduced the artificial lift efficiency, but also imposed various damages to the oil zones.Since 2002, a joint industrial project was set up to study the feasibility of performing water shutoff treatments in the openhole completion oil wells. The study involved evaluation of a high temperature polymer base water shut-off fluid for deep penetration of the fissure formation and a micro-fine cement system for sealing off the water entries. Based on this study, a cost-effective chemical treatment method was progressively developed. In 2005, the treatments were performed throughtubing with and without isolation packers.Two Candidate wells were having 6.5" open-hole size, at approximately 4,200 meter TD, and 150 deg C reservoir temperature. The water cut were 95% in one well and 30% in the other well. It was found that these two wells certainly had big difference in fluid injectivity, and original designed treatment was modified on site. This paper summarizes key lessons learnt including tool and packer conveyance, mixing and pumping of water shut-off fluids under offshore rig and wellsite conditions. It also shares a method of post treatment production evaluation and suggests operational change to improve the production.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.