Carbon intensity (CI) of oil and gas production varies widely across global oil plays. Life cycle extraction from certain unconventional plays (
We perform well-to-refinery calculations of CI for major unconventional oil plays in North America and conventional plays in Asia Pacific. This approach accounts for emissions from exploration, drilling, production, processing, and transportation. The analysis tool is an open-source engineering-based model called Oil Production Greenhouse Gas Emissions Estimator (OPGEE). OPGEE makes estimates of emissions accounting using up to 50 parameters for each modeled field. This model was developed at Stanford University. Data sources include government sources, technical papers, satellite observations, and commercial databases.
Applied globally, OPGEE estimates show highest values in areas with extensive flaring of natural gas and very heavy crude oils - heavy oils require large energy inputs (
Unconventional production, especially from light tight oil is the most significant new source of fossil fuels in the last decade. Under a wide variety of carbon constraints, oil usage will continue for many decades and increase in the near term. Operators, governments, and regulators need to be able to avoid "locking in" development of suboptimal resources and instead provide incentives for shale operators to manage resources sustainably. This approach provides quantitative measures of such actions. Oil producers must prepare by eliminating development of marginal projects, elimination of flaring and venting, optimizing hydraulic fracture treatments, using improved recovery methods (
References 1. Haugen, J.: "Rotary steerable system replaces slide mode for directional drilling applications," OGJ (March 2, 1998).
This paper presents the important effects of slowing down the oil production decline, increasing the sweep efficiency and improving the oil recovery by drilling horizontal sidetracks for the Huizhou 21-1, Huizhou 26-1 and Weizhou 11-4 oilfields in the South China Sea. And also analyzes the production performance of the eight horizontal sidetracks and the development effects in detail.
According to the practical production experience, it is economically and technologically feasible to produce the remaining oil and to improve the oil recovery by the sidetrack drilling technology during the middle and later production periods for the mature oilfield. The oil production rate of these eight horizontal sidetracks for single well is more than 2-3 times that of the average oil production rate of conventional well in the same reservoir. It indicates that this method has great potential and wide applying prospect to improve the development effect for sandstone reservoirs with strong edge and bottom water drive, especially during the middle and high water-cut periods. And also it is recognized that the accurate reservoir characterization and the detailed study of remaining oil in place are the basement for geological design of the horizontal sidetracks and can ensure success of the drilling.
Sidetrack drilling technology is to drill new wellbore by using the original straight wellhole. Its objective interval is the zone or area with low displacement efficiency, especially bypassed oil or unswept area. With the rapid development of drilling technology, such as coiled tubing, slim-hole drilling technology, the prospect of sidetrack drilling technology has been more and more widely. It can not only reduce the total drilling footage and the drilling cost, but also put to use more producing reserves, so as to increase the oil recovery factor. Especially in the middle or tail production period, drilling new directional hole or horizontal sidetracks by using the low production rate wells can effectively reduce the production decline, increase the reservoir potential productivity and improve the oilfield production effect.
The objective interval of sidetrack drilling is always the zone with rich remaining oil and relatively high oil saturation, so the productivity of the new sidetrack is high in most cases even to flow. Generally, one or more sidetracks can be drilled from one old wellbore. According to the information from oilfields in the world, it can increase the oil recovery factor by 5~8% OOIP or more by using horizontal sidetracks.
The Huizhou 21-1, Huizhou 26-1 and Weizhou 11-4 oilfields are located in the South China Sea, they are mainly of marine sedimental sandstone with strong edge water and bottom water drive. However the sweep efficiency of these three oilfields is not high due to the different geological characteristics and the heterogeneity of each reservoir. So still much oil can't be produced. One of the economic and effective methods is drilling horizontal sidetracks by using the old wells of high water-cut. By the end of 1999, the eight horizontal sidetracks have been drilled in these three oilfields, and all of them have achieved good production effects. The basic reservoir parameters and the production status for eight horizontal sidetracks are given in Table 1 and Table 2. As shown by experience with eight horizontal sidetracks, this paper describes that the application of drilling horizontal sidetracks in improving oilfield development effects, such as enhancing the oil production rate, enlarging the drainage area, reducing the water coning and increasing the oil recoverable reserves. And it also concluded that horizontal sidetrack drilling technology is one effective method to reduce the development cost, increase the controllable oil-bearing area of individual well and boost the hydrocarbon production rate.
DEVELOPMENT OF BOTTOM WATER-DRIVE RESERVOIR IN THE PEARL RIVER MOUTH BASIN Zhai Long Shen, China Offshore Oil Nanhai East Corporation; Fang Zhi, China Offshore Oil Nanhai East Corporation; Duan Cheng Gang, China Offshore Oil Nanhai East Corportion Abstract. The offshore bottom water-drive reservoirs in the Pearl River Mouth Basin have an excellent quality of high permeability, low oil viscosity, and extensive aquifer that give high productivity. Most of them have been put on stream, and successfully developed. The recoveries of these reservoirs were improved by capturing their geological features and the movement of the water-oil contact, with reservoir simulation as an important tool in the optimization of the offshore reservoir management. Upon the production performance of these bottom water-drive reservoirs, the initial development plans were adjusted to maximize the production from these reservoirs. On one hand, these reservoirs were depleted with a high depletion rate by fully utilizing the existing infra- structure. The high deleption rate shortens the field production life, reduces the operating cost and maximizes profit of the fields. On the other hand, the high productivity and strong aquifer support become a major concern in the development design of economically marginal bottom water-drive reservoirs, efforts were made to reduce the investment in facilities by simplifying the production system and make the development of such reservoirs viable. Development cases of the bottom water-drive reservoirs discussed below come from Huizhou oilfields. R ES E RVO I R CHAR ACTE R IST1 CS Bottom water-drive reservoirs found in the Huizhou fields are simple, low dip anticlines with four-way closures. These structures were developed upon their basement without obvious natural bar- riers or faults. The marine sandstones so developed were inferred to be beach sands, barrier bars, long- shore bars, etc. Sandbodies, generally well cemented, readily distinguishable from log responses cover a large area. Thus, the sands are usually associated with large aquifers. Sandstone formations are excellent in quality with an averaged core porosity and core permeability over 20% and 100 md respectively. Some porous sands have a core permeability over 10 darcies. Reservoir oil column on an averaged basis is about 15 meters. Very high effective permeability is also interpreted from drillstem tests, extended drillstem tests and early production tests. All evidences have confirmed that the subjected bottom water-drive reservoirs are highly productive. Oil contained in the reservoirs has a gravity of about 30" API with extremely low gas-oil ratio. Vis- cosity of oil is less than 5 cp's and its bubble point pressure is below 300 psi. As a result, the reservoirs can be depleted with large drawdown when artificial lifting is implemented. THE FIRST DEVELOPMENT Huizhou 21-1 oil field is the first oil field put on stream in the region. It cons