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Safari, Alireza R. (Mehran Engineering and Well Services Company) | Panjalizadeh, Hamed (Mehran Engineering and Well Services Company) | Pournik, Maysam (University of Texas Rio Grande Valley) | Jafari, Hamed (Mehran Engineering and Well Services Company) | Zangeneh, Alireza (Mehran Engineering and Well Services Company)
Summary The accomplishment of matrix stimulation in highly contrasted permeability reservoirs is critically dependent on diversion. Consequently, assessment of the diversion performance is a key to determine the success of stimulation. However, there are still doubts on the evaluation of diversion effectiveness, especially in long‐interval heterogeneous reservoirs. When a diverter enters the formation, a hump in the surface pressure curve is usually expected. Then, it can be interpreted as supporting evidence for diversion. However, this is a simplification of the fluid‐diversion process. It could be possible that a hump is not observed during a diversion stage, although it is effective. Therefore, what should be done? To overcome this challenge, we propose a more‐accurate diversion‐evaluation method and validate it with available matrix‐stimulation data. Three methods were introduced in the literature to evaluate matrix‐stimulation performance: Paccaloni, Prouvost, and Chan [inverse injectivity (i.e., Iinv)] methods (Prouvost and Economides 1987, 1989; Paccaloni and Tambini 1993; Chan et al. 2003). The latter is easy to use and accurate, which accounts for transient flow effects. In this paper, the inverse injectivity method is modified and validated with the real data of two matrix‐acidizing operations in a gas/condensate field. The performed modifications in the evaluation process include a bottomhole‐pressure‐calculation procedure, which is validated with available drillstem‐test (DST) matrix‐stimulation data, and simultaneous utilization of Iinv and its derivative plot. Humps in the Iinv plot, which can be interpreted as diverter performance, are sometimes so small that it is difficult to distinguish the diverter effect from possible noises in the data. Here, the derivative plot of Iinv is used as a complementary tool to improve the interpretation process. Results indicate that for both wells in this study, the modified Iinv shows clear humps when diverters enter the reservoir. In addition, exactly when Iinv builds up, a sign change in the derivative plot is observed. This shows that these two parameters have a confirming behavior. Finally, pre/post‐stimulation production data were used to practically prove the calculations behind the method. Here, the target of design was to divert stimulation fluids to the low‐permeability bottom layer because it was both a high-pressure and high-hydrocarbon reserve. Per production‐logging data, the majority of production before stimulation was originated from a sublayer. In the first operation, with the rare appearance of surface pressure humps, Iinv and its derivative showed satisfactory outputs of diversion occurrence. After stimulation, production logging confirmed the diversion of flow and nearly uniform production across the targeted interval. Hence, this indicates that the modified method accurately demonstrates the performance of the diversion system in acidizing operations with long perforated intervals, even if there is a rare distinct pressure hump in the surface. Therefore, this could be adapted either for cases where there is no access to the production logging or for the cases in which the hump in surface pressure is not observed.
Iran's national oil company is offering investment opportunities in 50 fields to global bidders, its first effort to do so since the 2015 pact with world powers that lifted nuclear-related sanctions against the country. Following an announcement by the Petroleum Ministry on 16 October that it would invite foreign companies to bid on field projects, the ministry the next day disclosed that 29 oil fields and 21 gas fields would be offered for bidding. International companies were given a 19 November deadline to submit applications, and the announcement of companies that qualify for bidding is slated for 7 December. The bid round is expected to open in January or February of next year. Iran's objective is to attract between USD 70 billion and 100 billion in foreign investment in its upstream oil and gas sector, and the country hopes to raise between USD 20 billion and 30 billion of that from the initial group of fields it has listed.
Summary Since its discovery in 1971, numerous matrix stimulations have been performed in South Pars field. However, there are still various challenges surrounding stimulation job design and evaluation methods. To tackle these issues, 16 matrix operations were selected to be analyzed from different phases of the development project of the reservoir. The objective of this study is to introduce an efficient interpretation method to determine optimum treatment volume (gal/ft), compare the effectiveness of diverters, calculate stimulation ratio (SR), and forecast post-acid production behavior from surface treatingdata. The modified inverse injectivity (Iinv) method, which is fully discussed by Safari et al. (2020), is used in this study. The obtained data were analyzed in terms of Iinv decreasing trend, Iinv humps, and pre-/post-acid Iinv during the stimulation process. In addition, pre-/post-stimulation surface testing data are gathered and analyzed. These data are coupled with post-acid Iinv to find a correlation to predict production behavior of treated wells. SR is defined as the ratio of pre-acid Iinv to post-acid Iinv of a treated well. Finally, SR values are validated with available production logging tool (PLT) data from two stimulation operations. First, the obtained results indicated that optimum treatment volume (gal/ft) of acid depends on well conditions. It means that wells with high initial formation damage require more volumes of stimulation fluids. In this regard, wells treated with 27/27 gal/ft treatment volume design [27 gal/ft 28% hydrochloric acid (HCl) and 27 gal/ft 15% viscoelastic surfactant (VES)] were understimulated. Although treatment volume design of 53/53 gal/ft seems to be adequate for low-skin wells, higher treatment volume (gal/ft) would further enhance productivity of highly damaged wells. This result was confirmed by stimulation of a damaged well with treatment volume of 60/60 gal/ft. Finally, the most reliable design applied in the field so far is the 70/70 gal/ft treatment volume. Second, Iinv analyses depicted that better diversion is observed in wells with lower injectivity and higher damage. At the next step, the calculated SR values showed an average deviation of less than 10% from downhole PLT data. Ultimately, the produced results demonstrated that there is a direct relation between the post-acid Iinv and surface drawdown in this field. Therefore, production behavior of treated wells can be correlated by having access to post-acid Iinv. The novelty of this work pertains to use of surface treating data recorded during a stimulation operation to generate Iinv and its associated analysis curves to evaluate performance of matrix stimulation operations. By applying this method, optimum volume of acid and diverter, diversion effectiveness, SR, and an estimation of post-acid surface drawdown can be obtained from the simple surface treating data. The secondary-produced data could lead to a better understanding of carbonate reservoir behavior during matrix stimulations such as in the South Pars field.
Iran's oil and gas sector has been significantly affected by the introduction and tightening of international sanctions in recent years, and the signing of the Joint Comprehensive Plan of Action (JCPOA) last July represents a significant step forward in terms of normalizing the country's relations with the global community. It also provides significant upside potential for Iran's oil and gas sector, both in terms of upstream drilling and production and oilfield services, and the maintenance and development of downstream infrastructure. In anticipation of its re-entry into the global market, Iran has produced a list of 50 oil and gas projects worth an estimated USD 185 billion that it intends to develop once the international sanctions have been removed. These projects will be introduced at a planned conference to be held later this month in London and will be auctioned to secure much-needed foreign investment. The projects listed for auction include the North Pars, Golshan, and Ferdowsi gas field developments, and a number of international oil companies, including BP, Shell, and Eni, have expressed interest in re-entering the market.
The re-emergence of Iran as a full player in the global oil and gas market is a major development and would be so under any market conditions. While the concerns are justified, the most important global dimensions of Iran's return to the market have to do with the country's long-term oil and gas potential. The recently implemented Joint Comprehensive Plan of Action (JCPOA), which is agreed to by China, France, Germany, Russia, the United Kingdom, the United States, the European Union, and Iran, lifts nuclear-related sanctions against Iran to restore the country's access to world oil and gas markets and its freedom to seek international investment in its industry. Imposed in December 2011 and the first half of 2012 in connection with Iranian nuclear activity, the sanctions placed restrictions on Iran's central bank, Iranian imports, and the country's access to international shipping insurance. As the sanctions took hold, Iran's production of crude oil and noncrude liquids fell from 4.4 million B/D in 2011 to an average of 3.6 million B/D over the next 3 years.
Panjalizadeh, Hamed (Mehran Engineering & Well Services Co) | Safari, Alireza (Mehran Engineering & Well Services Co) | Kamani, Mehrdad (Mehran Engineering & Well Services Co) | Jafari, Hamed (Mehran Engineering & Well Services Co)
Abstract Since its discovery at 1971, numerous matrix stimulations were performed in South Pars field. However, there are still various challenges on stimulation job design and evaluation methods. In order to tackle these issues, fifteen matrix operations were selected to be analyzed from different phases of development project of the reservoir. The objective of this study is to introduce a new approach to figure out optimum acid volume (gal/ft), compare the effectiveness of diverters, calculate stimulation ratio (SR), and forecast post-acid production behavior from surface treating data. Modified inverse injectivity (Iinv) method, which is fully discussed by Safari et al. (2020), is utilized in this study. Obtained data were analyzed in terms of Iinv decreasing trend, Iinv humps as well as pre/post-acid Iinv during stimulation process. In addition, pre/post-stimulation surface testing data are gathered and analyzed. These data are coupled with post-acid Iinv to find a correlation to predict production behavior of treated wells. SR is defined as the ratio of pre-acid Iinv to post-acid Iinv of a treated well. Finally, SR values are validated with available PLT data of two stimulation operations. Obtained results indicate that optimum gal/ft of acid depends on well conditions. In this regard, wells with high initial formation damage require more volumes of acid. In this regard, wells treated with 27/27 gal/ft design (27 gal/ft 28%HCl and 27 gal/ft 15%VES, i.e. Visco Elastic Surfactant,) were under-stimulated. Although, 53/53 gal/ft design seems to be adequate for low-skin wells, higher gal/ft would further enhance productivity of highly damaged wells. This result was confirmed by stimulation of a damaged well with 60/60 gal/ft design. Finally, the most reliable design applied in the field is 70/70 gal/ft so far. Iinv analyses depict that better diversion is observed in wells with lower injectivity and higher damage. Generally, the magnitude of Iinv humps, which represents as a supporting evidence for diversion, decreases as stimulation proceeds. Furthermore, fiber–laden VES diverter exhibited better diversion than VES alone. Surface post acid drawdown at a specific production rate, e.g. 50 MMSCFD, is defined as the difference between shut-in and flowing wellhead pressures. Obtained results demonstrate that there is a direct relation between the post-acid Iinv and surface drawdown in this field. Therefore, production behavior of treated wells can be correlated by having access to post-acid Iinv. Ultimately, calculated SR values demonstrated average deviation of less than 10% with downhole PLT data. The novelty of this work pertains to utilization of the Iinv method to evaluate performance of matrix stimulation operations. By applying this method, optimum volume of acid and diverter, diversion effectiveness, stimulation ratio as well as a prediction of post-acid surface drawdown can be obtained from surface treating data. The proposed methodology led to get better understanding of South Pars reservoir behavior during matrix stimulations. The same methodology can be applied to other carbonate reservoirs, too.
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 200135, “A Comprehensive Method for Diverter-Performance Evaluation During Stimulation of Long-Interval Heterogeneous Reservoirs: A Case Study” by A.F. Safari and H. Panjalizadeh, Mehran Engineering and Well Services Company; M. Pournik, SPE, The University of Texas Rio Grande Valley; and H. Jafari and A. Zangeneh, Mehran Engineering and Well Services Company, prepared for the 2020 SPE Conference at Oman Petroleum and Energy Show, Muscat, Oman, 14-16 September. The paper has not been peer reviewed. Assessment of diversion performance is key to determining success of stimulation. Doubts remain, however, regarding the evaluation of diversion effectiveness. As diverter enters the formation, a hump in the surface pressure curve usually is expected. It then can be interpreted as supporting evidence for diversion. This, however, is a simplification of the fluid-diversion process. Such a hump may not be observed during a diversion stage even when the process is effective. In the complete paper, the inverse-injectivity method of evaluating matrix-stimulation performance is modified and validated with real data of two matrix-acidizing operations in a gas-condensate field. South Pars Gas Field In 1971, an enormous gas reservoir, the North Dome Field, was found in the Qatar Dome structure of the Persian Gulf. In the years since, surveys have highlighted the existence of abundant amounts of gas and condensate accumulations in a huge dome. This single gas-bearing structure is delineated by the geographical borders between Iran and Qatar in the Persian Gulf. According to one recent estimate, almost 19% of the world’s gas rests in this vast basin. The field includes two independent gas-bearing formations, Kangan (Triassic) and Upper Dalan (Permian). Each formation is divided into layers separated by impermeable barriers, namely K1, K2, K3, and K4. The K1 and K3 layers mostly are formed of dolomites and anhydrites. Layers K2 and K4 possess better reservoir specifications (i.e., highly permeable and porous, consisting of limestone and dolomite). An anhydrite-composed layer, the Nar Member, separates Layer K4 from the underlying K5 layer, which has nonsatisfactory reservoir qualities. Methodology In this study, the inverse injectivity and its integral and derivative plot are coupled with results of production logs to evaluate diverter-system performance in two real acidizing operations performed in the South Pars field. What makes this work different is the complexity of the treated reservoir in terms of the number of layers (four distinct formations), formation heterogeneity, and long perforation intervals (an approximately 1,000-ft net interval). The productivity index is a measure of the well’s production potential and is defined as a ratio of the total liquid surface rate to the pressure drop at the midpoint of the producing interval. Because the direction of flow in this case is in a direction opposite that of production, this parameter is considered as the reverse of the productivity index and is called inverse injectivity. In this study, a program is written to calculate modified inverse injectivity during two real matrix stimulations performed in the field. The equations used in this method are provided in the complete paper.
Assessment of diversion performance is key to determining success of stimulation. Doubts remain, however, regarding the evaluation of diversion effectiveness. As diverter enters the formation, a hump in the surface pressure curve usually is expected. It then can be interpreted as supporting evidence for diversion. This, however, is a simplification of the fluid-diversion process. Such a hump may not be observed during a diversion stage even when the process is effective.
Bahrami, Esmaeil (Mehran Engineering and Well Services Co.) | Seyednia, Mahbod (Mehran Engineering and Well Services Co.) | Mosallaie Barzoki, Ali Akbar (Mehran Engineering and Well Services Co.) | Zangenehvar, Alireza (Mehran Engineering and Well Services Co.) | Rabbani, Seyedebrahim (Mehran Engineering and Well Services Co.)
Abstract Ship collision with offshore platform is one of the rare events in oil and gas industry and generally associates with huge physical and financial damage. An oil tanker collided with a jacket in the South Pars gas field and caused tough conditions for the operator to restore the jacket and wells to their original state. The crucial stages after the accident were killing a perforated well, wreck removal and cutting the wells below the section they had been bent or distorted and finally the wells abandonment by cementing coiled tubing operation on a dynamic positioning barge. This paper focus on engineering design of a platform for coiled tubing injector head and pressure control equipment on the barge as well as finding a way that coiled tubing string pass through the gap between the platform and the underwater cut point of wells. For this purpose, a deck was proposed to build on the barge having a heavy duty flexible steel pipe extended from the deck to inside the wells cut point. Various measures should be implemented to design this structure in order to have an operational safe method. The structure had to have sufficient strength to resist the forces applied on it especially during the operation in the predominant weather condition of Persian Gulf in the monsoon season. Therefore, a comprehensive study was conducted to determine stresses applied on the structure subjected to different types of wave velocities using finite element method. The engineering design and simulation led to construct the proposed deck extending over the port side of the barge and elevating between the main deck and mezzanine deck with a long 4" flexible steel pipe at its bottom. In order to verify the engineering design and simulation before the operation, the structure load tested up to 40 metric tons. This paper will peer over the challengeable engineering design of the deck for coiled tubing well abandonment under the condition of insufficient offshore facility.
Bahrami, Esmaeil (Mehran Engineering & Well Services Co.) | Zangenehvar, Alireza (Mehran Engineering & Well Services Co.) | Mohseni, Arman (Mehran Engineering & Well Services Co.) | Mortazavizadeh, Seyedmorteza (Mehran Engineering & Well Services Co.) | Safari, Alireza (Mehran Engineering & Well Services Co.) | Aryanfar, Yasha (Mehran Engineering & Well Services Co.)
Abstract Cement behind casing, as the critical component of well integrity is a real challenge all over the world. Despite the efforts drilling operators and service providers dedicate to this phase of well construction in the South Pars gas field, final set cement quality does not establish zonal isolation in 9 5/8" casing and 12 1/4" openhole section. In order to study this issue, twenty-four wells have been analyzed based on theoretical analysis, close hands-on operations and track record of cementing in the field. Data were acquired from the daily drilling reports, data acquisition system of cement units, mud logging records, daily mud reports, cement slurry laboratory test sheets and wireline log records. The main effective factors on cement quality have been studied in four groups namely: well preparation, slurry design, mud removal and post-cementing practices. Good and poor quality cement in all wells have been compared with actual field parameters using a cementing displacement simulator software. Structural stress model has also performed for one of the wells whose cement was prone to be impacted by post cementing practices. Results have been obtained over one year of parallel laboratory testing, field experience, simulation and evaluation. The simulations results illustrate turbulent flow is not practical for cementing of this section and effective laminar flow technique shows an efficient alternative, however all criteria of this technique could not have been fully met due to some well restriction. The results reveal mud removal parameters in terms of casing centralization have significant effects on the final cement quality in this field. Cement quality devastation persisted even in cases where the cement slurry properties were modified and used in four wells in order to evaluate slurry design impact degree on final set cement quality. The stress model results illustrate that imposed stress on the well exceeds the compressive and tensile strength of the cement sheath. These results reinforce the idea that mud removal and post cementing practices govern the cement quality in the field. This paper is a comprehensive study of all effective parameters on cement quality in 9 5/8" casing cementing and highlight the main sources of cement quality devastation in the field and it can be used as a guideline for cementing similar cases around the world.