Farog, Ali (SUDAPET) | A.Mustafa, Haytham (SUDAPET) | Mukhtar, Enas (SUDAPET) | Elblaoula, Husham (SPC-OEPA) | A. Yassin, Badreldin (SPC-OEPA) | Tagwa, Musa (Sudan University of Science and Technology) | Mucharam, Leksono (ITB) | Abdalla, Fadul (GNPOC)
Bamboo field is located in block 2A Muglad Basin covers an area of 144 Square km. It consists of multi block, multi-layered under-saturated sandstone reservoir of late Cretaceous ages barried at depth ranging from 1000 m to 1700 m with crude oil viscosity ranges from 70 cp to 3000 cp. The total Field STOIIP and Recovery Factor (RF) are currently estimated at around 506MMSTB and 18% respectively through primary depletion. Up to date; the field had recovered more than 75% of the EUR.
The field initially produced around 20,000 STB/Day with early water breakthrough and very minimal gas production rate until today. However the production rate declined rapidly when the water production rate increased. Major factors that contributed to this problem are possibly due to the fingering and water conning. Currently the field is producing around 8000 STB/Day with water cut around 80% and keeps increasing.
Schemes in enhancing and prolonging the already decline production and diminishing reserves strategically call for timely implementation of Enhanced Oil Recovery (EOR) process. Among various Enhanced Oil Recovery (EOR) process and techniques, Bamboo reservoirs appear especially amenable to thermal injection process. But Sudapet, ITB and PERTAMINA (an especial study) came up with different solution which is Huff and Buff of Chemical EOR, This proved to be one of the practical, promising and potential options in enhancing the recovery factor in Bamboo Field.
This paper will discuss the lab study scope, includes the core sample, fluid sample, phase behaviour test, spontaneous Imbibition Test, Compatibility test, Viscosity Mixture and core flood, well selection analysis as well as the implementation of SEMAR as pilot project in Bamboo Oil Field.
After implementation of the pilot as Huff and Puff in three wells the results show that about 18,000 STB of oil gained from adjacent wells, which indicate that SEMAR is very interesting to be evaluated for further steps in chemical EOR implementation for continuous Injection.
Conventional pressure transient testing, using a pressure gauge positioned at a fixed depth in a well, has historically been the main source of permeability and skin estimation in formations. However, if a well is completed as a multi-layer commingled producer, then this conventional approach makes it difficult to measure the permeability and skin of individual layers.
Greater Munga field of the Greater Nile Petroleum Operating Company (GNPOC) in Sudan has several wells that commingle production from the Aradabia, Bentiu-2 and Bentiu-3 formations. These formations are highly variable in terms of the reservoir properties, oil types and pressure regimes. A selective inflow performance (SIP) test was carried out during production logging (PL) jobs in some of these wells and it indicated that the productivity index (P.I.) of the individual layers varies widely, ranging from 1.5 to 15 b/d/psi. This illustrated the need for a method to estimate the permeability and skin of each layer. This information was needed for reservoir model calibration, well
productivity prediction, low productivity diagnosis and remedial action selection.
Two solutions were proposed to GNPOC; use the conventional technique of isolating each layer and testing it separately or carry out a commingled multi-layer transient (MLT) test with a PL tool. In an MLT test, in addition to the normal PL runs, individual pressure transient stations are also recorded at the top of each contributing layer. The MLT test measures the flow rate and wellbore pressure above each producing layer for different surface flow rates during the infinite-acting phase. These individual layer flow rates and pressure transients are used to calculate the individual layer properties.
GNPOC decided to go in for the MLT testing option and two wells were analyzed. In the first well, MLT testing showed that one of the layers had a very high permeability compared to the other layers. It depleted much faster and had early water breakthrough. Consequently a water shut-off job is planned for this layer. In the second well, MLT analysis showed that the upper layer had poorer permeability as compared to the lower layers. However, this layer holds good oil reserves. Hence, this well is a good candidate for future side tracking into the upper layer, in order to exploit the untapped reserves in this layer.
In this paper, we will discuss the MLT testing technique, introduce a workflow for the analysis, and then will discuss the results of the analyses for two examples from GNPOC. Based on the success of these cases, multi-layer transient testing is estabilished as a preferred testing technique in this complex reservoir environment.
Greater Unity a multilayered clastic reservoir in Sudan is a conglomeration of number of fault blocks- lacustrine deposits of late cretaceous age. Reservoir characteristics are mostly heterogeneous with varying degree of heterogeneities both vertically and horizontally. Reservoirs are highly undersaturated and have poor aquifer support. Rapid pressure decline was observed in early phase of production, severely affecting the performance of pumps resulting into frequent failures and causing sharp production decline. Water injection in low pressure mode was resorted in some blocks. Failure rates of ESP and PCP reduced significantly as dynamic fluid level (DFL) increased noticeably, provided sufficient submergence, and improvement in efficiency of the pumps.
Significant decline in injectivity in Aradeiba formation compelled to change the strategy of injection. Step rate tests were the guiding factor for selecting the low and high pressure injections and also stimulation. Paper discusses application of diagnostic methods like Hall plot, Jordan plot and other empirical relations using Pressure, injection and production data for understanding and improving the injection process. Profile modification for better conformance control gained early importance in view of smaller sizes of the pools.
Nonparametric statistical method known as Spearman rank analysis has been used to understand and analyze the degree of communication between injectors and producers. This analysis quickly identifies the communication between injectors and producers, or lack of communication and helps in understanding the response of injection. Preferential flow trends are reflected by the correlation in rates between injectors and producers along with lead time response of injection on production.
Paper illustrates the important ingredients which can add value to asset and improve the reserves and overall development strategy. Therefore, it is highlighted that success and failure of water injection project depends on why, when, where, what, how and how much to inject, plus what will happen to the formation once the water injection starts.
Tewari, R.D. (GNPOC) | Raub, M.R.B.A. (GNPOC) | Omar, M.I. (QP) | Fenghan, B. (GNPOC) | Moris, M. (GNPOC) | Jelani, J. (PRSS) | Ramachandran, S. (AWT) | Fooks, A.L. (AWT) | Peden, J.M. (AWT) | Montague, Eamonn T. (Brunei Shell Petr. Sdn. Bhd.)
This paper describes the importance of well construction & well integrity and its relationship to reservoir management. Productivity enhancement studies in combination with reservoir simulation modeling on the Greater Heglig fields have revealed that well performances and production related problems were largely related to poorly designed wells and poor cementing practices. As a result, water channeling and cross flow across wellbore dominated true well performance characteristics contributing to very high water cuts in the majority of the producers in Greater Heglig fields. Separating the mechanically induced well behaviour from reservoir behaviour helped history matching the wells greatly, findings of which were subsequently validated during the study through running of ultra sonic imaging tool. The ultra sonic logging campaign proved the existence of channels, micro annuli's and cross flow across the wellbore causing a "water channeling phenomena" of up to 90% water cut across majority of the wells. As part of the productivity enhancement program for the Greater Heglig fields, a total of 23 sidetrack candidates have now been identified to capture the remaining developed reserves of ca. 30.0 MMstb, which will otherwise remain unproducible from the existing wellbore's. In addition to this, fit for purpose sidetrack well designs and construction together with good cementing practices will be required to ensure well integrity to improve reservoir management of the Greater Heglig fields.
Copyright 2005, Society of Petroleum Engineers This paper was prepared for presentation at the SPE International Improved Oil Recovery Conference in Asia Pacific held in Kuala Lumpur, Malaysia, 5-6 December 2005. This paper was selected for presentation by an SPE Program Committee following review of information contained in an proposal submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to a proposal of not more than 300 words; illustrations may not be copied. The proposal must contain conspicuous acknowledgment of where and by whom the paper was presented. Abstract Bamboo West, a heavy oil (API Gravity 18-20) field is located in Muglad basin of south-central Sudan.