The Iceland Deep Drilling Project: a search for deep unconventional geothermal resources

The Iceland Deep Drilling Project (IDDP) is a long-term program to improve the economics of geothermal energy by producing supercritical hydrous fluids from drillable depths. Producing supercritical fluids will require the drilling of wells and the sampling of fluids and rocks to depths of 3.5–5 km, and at temperatures of 450–600 °C. The IDDP plans to drill and test a series of such deep boreholes in the Krafla, Nesjavellir and Reykjanes geothermal fields in Iceland. Beneath these three developed high-temperature systems frequent seismic activity continues below 5 km, indicating that, even at supercritical temperatures, the rocks are brittle and therefore likely to be permeable, even where the temperature is assumed to exceed 550–650 °C. Temperature gradients are greater and fluid salinities smaller at Nesjavellir and Krafla than at Reykjanes. However, an active drilling program is underway at Reykjanes to expand the existing generating capacity and the field operator has offered to make available one of a number of 2.5 km deep wells to be the first to be deepened to 5 km by the IDDP. In addition to its potential economic significance, drilling deep at this location, on the landward extension of the Mid-Atlantic Ridge, is of great interest to the international science community. This paper examines the prospect of producing geothermal fluids from deep wells drilled into a reservoir at supercritical temperatures and pressures. Since fluids drawn from a depth of 4000–5000 m may prove to be chemically hostile, the wellbore and casing must be protected while the fluid properties are being evaluated. This will be achieved by extracting the fluids through a narrow retrievable liner called the “pipe”. Modelling indicates that if the wellhead enthalpy is to exceed that of conventionally produced geothermal steam, the reservoir temperature must be higher than 450 °C. A deep well producing 0.67 m³/s steam (2400 m³/h) from a reservoir with a temperature significantly above 450 °C could, under favourable conditions, yield enough high-enthalpy steam to generate 40–50 MW of electric power. This exceeds by an order of magnitude the power typically obtained from a conventional geothermal well in Iceland. The aim of the IDDP is to determine whether utilization of heat from such an unconventional geothermal resource at supercritical conditions will lead to increased productivity of wells at a competitive cost. If the IDDP is an economic success, this same approach could be applied in other high-temperature volcanic geothermal systems elsewhere, an important step in enhancing the geothermal industry worldwide.     

河坝构造复杂工程地质问题与安全优快钻井技术对策

河坝构造钻井工程难度大,存在漏、塌、卡、涌、毒、硬、斜等问题,钻井效率低、周期长,需要在工程地质特征基础上,提高钻井工程工艺的针对性。本文在岩石力学实验基础上,建立工区岩石力学参数剖面,表明该构造地层岩石致密,抗压强度、抗剪切强度、硬度大,可钻性差。根据地层孔隙压力、坍塌压力、破裂压力剖面,开展井壁稳定性分析,表明该区纵向多压力系统,陆相地层坍塌压力高,易井壁失稳;海相地层异常高压,安全钻井液密度窗口窄,井壁力学稳定性差。结合工程地质特征,提出优化井身结构设计,优选气体钻井、泡沫钻井、垂直钻井、复合钻井、旋转导向钻井等钻井技术,优选钻头型号,优选钻井液,优选防漏堵漏技术等钻井对策。现场实钻证实,上述对策大幅提高了机械钻速,有效减少了钻井复杂情况,大幅缩短了钻井周期,实现了河坝构造海相超深气井优快钻井。     

Geochemical evidence of drawdown in the Cerro Prieto geothermal field

Some wells of the Cerro Prieto geothermal field have undergone changes in the chemistry of fluids produced which reflect reservoir processes. Pressure decreases due to production in the southeastern part of the field have produced both drawdown of lower chloride fluids from an overlying aquifer and boiling in the aquifer with excess steam reaching the wells. These reservoir changes are indicated by changes in fluid chloride concentrations, Na/K ratios and measured enthalpies and by comparisons of aquifer fluid temperatures and chloride concentrations calculated from enthalpy and chemical measurements. Fluid temperatures have not been greatly affected by this drawdown because heat contained in the rock was transferred to the fluid. When this heat is exhausted, fluid temperatures may drop rapidly.     

关于加快发展我国油基钻井液体系的几点看法

油基钻井液具有抗高温、抗盐钙侵、有利于井壁稳定、润滑性好和对油气层损害程度小等优点.国外早在20世纪60年代,就十分重视油基钻井液技术的开发与应用,现已广泛作为钻深井、超深井、海上钻井、大斜度定向井、水平井和水敏性复杂地层及储层保护的重要手段.国外油基钻井液体系及配套技术比较成熟,国内在油基钻井液方面尽管开展了一些工作,但应用较少,还没有形成体系.目前,国内非常规油气资源的开发已经启动,对油基钻井液有了迫切需求.我国应在油基钻井液应用方面尽快行动起来,在借鉴国外经验和国内初步实践的基础上,首先开展油基钻井液的应用,在应用中积累经验、完善体系,并通过油基钻井液处理剂(降滤失剂、提黏切剂、封堵剂及润湿剂)的研制,逐渐形成具有国内特点,能够满足现场需要的油基钻井液体系,以及钻井液回收处理循环再利用的配套设备与方法.同时,开展油基钻井液高温下流变性、稳定性研究,以形成系统的流变性控制方法,为油基钻井液体系的应用提供理论支撑,促进国内页岩气等非常规油气资源的开发.     

页岩气水平井钻井液技术的难点及选用原则

我国页岩气资源勘探开发已全面铺开。针对页岩气的成藏特征,页岩气开发以浅层大位移井、丛式水平井布井为主。由于页岩地层裂缝发育、水敏性强,长水平段钻井中不仅易发生井漏、垮塌、缩径等问题,且由于水平段较长,还会带来摩阻、携岩及地层污染问题,从而增大了产生井下复杂情况的几率。解决井壁稳定、降阻减摩和岩屑床清除等问题是目前页岩气水平井钻井液选择和设计的关键。选择页岩气水平井钻井液的原则是确保井壁稳定、润滑、防卡和井眼清洗。油基钻井液可提高水润湿性页岩的毛细管压力,防止钻井液对页岩的侵入,从而有效保持井壁稳定,同时还具有良好的润滑、防卡和降阻作用,是国内外目前采用最多的钻井液体系。当采用水基钻井液的时,利用低活性高矿化度聚合物钻井液或CaCl2钻井液以降低页岩和钻井液相互作用的总压力;采用浓甲酸钾、Al3+盐,可以通过脱水、孔隙压力降低和影响近井壁区域化学变化的协同作用产生良好的井眼稳定作用;对于有裂隙、裂缝或层理发育的高渗透性页岩应使用有效的封堵剂进行封堵;但对于强水敏性页岩地层,水基钻井液在抑制性方面仍然存在局限性。从环境保护的角度出发,甲基葡糖苷钻井液在井壁稳定机理方面与油基钻井液相似,未来可望作为有效的钻井液体系之一。随着以页岩气为代表的非常规油气资源的不断开发,为了满足安全钻井和环境保护的需要,未来页岩气水平井钻井液技术的研究应围绕高效、低成本水基钻井液和低毒油基钻井液来展开。     

复合盐饱和盐水钻井液在利97井中的应用

利97井是胜利油田布署的一口钻探盐下油气藏的重点探井,共钻遇3套盐膏层,盐膏层总厚度达600m,其井段岩性主要为盐膏岩、膏泥岩、纯盐岩及红色、灰色泥岩。根据该井地质特点和施工要求,配制复合盐饱和盐水钻井液体系,并进行热稳定性和抗污染性实验,在该井三开井段(2850～3915m)应用,取得良好效果。有效抑制了泥岩段地层黏土矿物的水化膨胀,钻井过程中无掉块,起下钻顺利;盐膏层钻井过程中,用Na2SO4控制钻井液中Ca2+含量,很好地控制了钻井液流变性和滤失量,减少了采用纯碱控制Ca2+含量对钻井液流变性造成的不利影响;用饱和盐水钻井液控制Cl-的浓度,使其一直处于饱和状态,钻井液未对井壁溶蚀,电测解释井眼相对规则;三开钻进、电测、完井及取心都非常顺利(盐膏层取心2次),表明复合盐饱和盐水钻井液体系适合该区块的钻井施工,值得推广应用。     

Reservoir performance of the Geysers Field

The Geysers Field, located in Northern California, has an installed generating capacity of 502 MWe. Total withdrawal rate is approximately 8-5 million lb/h of steam from 95 wells. Four new generating plants are currently under construction, which will bring the installed capacity to 908 MWe by 1979.The reservoir rock consists of naturally fractured graywacke, a very competent rock with low interstitial porosity and permeability. The reservoir contains dry steam with an initial pressure of approximately 514 psia at sea level datum. Static pressure gradient is that of saturated steam to the total depths of wells drilled to date.The initial development at The Geysers Field occurred in an area which has two shallow dry steam anomalies. Recent studies have shown that the steam in these anomalies is being fed through fractures connecting them with the deeper regional fracture system.Development of the regional system has created two distinct pressure sinks. The larger of the two pressure sinks is in the oldest and most developed portion of the field. This sink has grown larger with the addition of new production capacity. There is no pressure interference between the two sinks, but pressure interference between wells in a given pressure sink is very rapid. Pressure behavior at observation wells in these sinks resembles an ideal single-phase system with constant pressure boundaries.The expansion of the field has been the result of continued exploratory drilling and testing of new step-out wells. Based on the successful exploratory wells drilled to date, it is estimated that the generating capacity of The Geysers could reach 1800 MW by the mid-1980s.     

应用废弃油气井获得地热能

为了有效的利用现有的废弃油井和气井中存在的大量热能,建立了废弃油气井中循环流体的流动换热方程以及循环流体和岩石的热交换方程,运用数值模拟进行了求解,计算结果表明:循环流体的流量和地温梯度是影响换热量的两个最主要因素。地温梯度Tg分别为25、45和65℃/km时,最大换热量分别为184.12,394.22和604.96 kW。对于确定的地温梯度,总存在最优的流速使换热量或发电量最大;地热能采出系统能够长期稳定运行。对于Tg=45℃/km的工况,第一年和第八年末采出井口流体的温度分别为100.38和99.48℃;两井之间的最小间距应不小于20 m。     

国内页岩气开采技术进展

因页岩气开发具有资源潜力大、开采寿命长和生产周期长等优点,已成为当前能源研究的热点和突破口.自2009年以来,我国已在页岩气开发实验区钻井62口,其中24口井获得工业气流,这预示着国内页岩气资源开发全面铺开.页岩气储层与常规储层差异很大,必须采用先进技术,尤其是水平井钻井、完井及压裂技术,才能实现经济有效开发.介绍了国外页岩气开采技术以及国内近两年在页岩气钻井技术、钻井液技术、固井技术和压裂技术方面取得的经验,这些经验奠定了国内页岩气开发的技术基础.论述了页岩气开采面临的技术和环境问题,指出下一步页岩气技术发展方向.今后,需要结合国内页岩气藏特点,在借鉴国外新技术及国内经验基础上,通过工具研制、技术配套、方案优化,尽快完善适用于页岩气开发的水平井钻井技术;从流变性、封堵能力方面进一步完善油基钻井液体系,同时开展适用于页岩气水平井钻井的水基钻井液体系研究;针对页岩气水平井多采用油基钻井液的现状,进一步完善冲洗液、水泥浆体系及固井工艺技术.开发适合页岩气水平井多级压裂技术相关的井下工具、工作液和施工工艺,加强压裂裂缝动态监测,优化压裂设计.形成配套的钻井和压裂等作业过程中产生的废液、废水及废渣处理技术,重视贞岩气开采的环境污染评估,保证我国页岩气开发的健康发展.     

Lithological correlations of the cerro prieto wells, based on well - log interpretation

This paper presents the results of correlations of the geophysical well logs obtained from wells drilled at the Cerro Prieto geothermal field. From this correlation, a structural interpretation of the ‘receptacle’ holding the geothermal fluids has been obtained.Based on the temperature and electrical resistivity logs, the presence of two main geothermal reservoirs has been established. It was also found that most of the wells were completed such that production is obtained simultaneously from several sandy layers. In all probability this has created some mechanical problems in the wells in addition to a certain confusion in the interpretations based on fluid production data.An hypothesis is postulated about the deposition environment and the genesis of the reservoir, on the basis of which it is concluded that the reservoir is a paleochannel. It is also postulated that thinning of the basement rocks is the fundamental cause of the heat transmission to the reservoirs.Tables listing the correlating marker horizons for each well and maps showing the top of the two main reservoirs and the isopacks for the shallow one are presented. From these data have been inferred the areas showing the best possibilities for immediate geothermal development.     

Results from Le Mayet de Montagne project

An in-situ experiment on forced fluid flow through a granitic rock mass has been undertaken at Le Mayet de Montagne in Central France. The goal of this experiment is to circulate water between two 800 m deep boreholes separated from each other by about 100 m. The system has been designed to accommodate fluid flow of the order of 60 m³/h (15 l/s).The purpose of the tests is to investigate the possibility of hydraulically stimulating preexisting fractures in order to improve their hydraulic conductivity and create a heat exchanger with an effective area of the order of 200 000 m².The paper present results of preliminary work concerning

• •- the drilling of the wells by downhole air-percussion;
• •- reconnaissance of the rock mass;
• •- results from small scale injection tests.

The reconnaissance of the rock mass involves various logging techniques as well as in-situ stress determination. A new electrical log developed by Mosnier has been found to be very efficient for the mapping of fractures. Interpretation of sonic logs yields information concerning the hydraulic conductivity of these fractures. Hydraulic tests on pre-existing fractures are shown to provide reliable data for the in-situ stress determination.The efficiency of the small scale injection tests has been investigated through analysis of the seismo-acoustic activity induced by the injections. It is concluded that all those hydraulic fractures which were initiated at the well in directions different from that of the maximum horizontal principal stress had only a limited extension and that, away from the injection well, flow occurred along pre-existing, more permeable fractures.In addition, all the observed seismo-acoustic activity has been found to be caused by shear events. These events involve pre-existing fracture planes which intersect the walls of the main flow path, but no shear along the flow path itself was identified. This suggests that flow occurred along surfaces sub-parallel to the principal in-situ stress directions.     

Calcite deposition at Miravalles geothermal field Costa Rica

The calcite deposition problem at Miravalles has been studied since it was observed in the first three wells drilled on the slopes of the Miravalles Volcano. Long-term tests have been carried out to study reservoir characteristics. The change in the production behavior of the wells with the restriction imposed by the deposited calcite has been studied trying to evaluate and quantify the scaling problem. Work is being done on predictions of the deposition rate, location and distribution of the deposited mineral inside the wells. This work was compared with real data obtained from caliper logs of the wells before and after production. The feasibility of the first 55 MW power plant has been demonstrated. It was considered that the solution for the calcite problem is the “reaming during discharge of the wells” trying at the same time to minimize the cleaning interventions with a new well design. A long-term inhibitor test has been scheduled by the beginning of 1989. The economic evaluation of this test may affect the decision of reaming the wells as a solution for the feasibility of the first and subsequent power units. It is also believed, due to the thermodynamics and chemical characteristics of the extracted fluids, that it is possible to find a “non-deposition zone” which will permit the drilling of wells without a scaling problem.     

A borehole temperature during drilling in a fractured rock formation

Drilling in brittle crystalline rocks is often accompanied by a fluid loss through the finite number of the major fractures intercepting the borehole. These fractures affect the flow regime and temperature distributions in the borehole and rock formation. In this study, the problem of borehole temperature variation during drilling of the fractured rock is analyzed analytically by applying the approximate generalized integral-balance method. The model accounts for different flow regimes in the borehole, for different drilling velocities, for different locations of the major fractures intersecting the borehole, and for the thermal history of the borehole exploitation, which may include a finite number of circulation and shut-in periods. Normally the temperature fields in the well and surrounding rocks are calculated numerically by the finite difference and finite element methods or analytically, utilizing the Laplace-transform method. The formulae obtained by the Laplace-transform method are usually complex and require tedious numerical evaluations. Moreover, in the previous research the heat interactions of circulating fluid with the rock formation were treated assuming constant bore-face temperatures. In the present study the temperature field in the formation disturbed by the heat flow from the borehole is modeled by the heat conduction equation. The thermal interaction of the circulating fluid with the formation is approximated by utilizing the Newton law of cooling at the bore-face. The discrete sinks of fluid on the bore-face model the fluid loss in the borehole through the fractures. The heat conduction problem in the rock is solved analytically by the heat balance integral method. It can be proved theoretically that the approximate solution found by this method is accurate enough to model thermal interactions between the borehole fluid and the surrounding rocks. Due to its simplicity and accuracy, the derived solution is convenient for the geophysical practitioners and can be readily used, for instance, for predicting the equilibrium formation temperatures.     

A generalized multifluid optimal pressure for heat exchangers operating with supercritical fluid

Distinct thermophysical properties encountered in supercritical fluids operating near the critical point have made them strong candidates for working fluids in various engineering applications. Particularly due to the existence of heat capacity maxima near the critical point, heat transfer involving supercritical fluids and their employment in power generation systems have received special attention. In this paper, the existence of optimal operating pressures that maximize the global conductance of supercritical heat exchangers is demonstrated. Analysis of the behavior of the isobaric specific heat along the heat transfer process shows that optimal performance is achieved when the average isobaric specific heat is maximized. Consequently, optimal pressure maps can be created to assist heat exchanger design for various combinations of inlet temperatures and heat transfer rates. Furthermore, it is demonstrated that simple dimensionless groups can correlate—with a mean absolute error (MAE) of 0.0332—the optimal operating pressures of up to 122 different fluids. In addition, it is shown that the correlation is even stronger closer to the critical point and for separate classes of fluids, where MAE can be as low as 0.0103 for triatomic substances.     

Shallow submarine and subaerial, low-enthalpy hydrothermal manifestations in Punta Banda, Baja California, Mexico: Geophysical and geochemical characterization

The low-enthalpy geothermal system at Punta Banda (NW Baja California Peninsula, Mexico) has been studied because it might provide heat to future desalination plants in the city of Ensenada. Utilization of subaerial, intertidal and submarine hot springs is evaluated based on geochemical and geophysical data. The results of the geochemical studies show that the geothermal fluids have a major meteoric water component because seawater is not present at the subaerial springs and hot wells. The highest estimated reservoir temperature (140 °C) calculated using a silica geothermometer corresponds to the Agua Caliente intertidal manifestation, a promising area also identified by geophysics. Geothermometric calculations applied to the computed composition of the thermal end member yield a reservoir temperature of 137 °C. Cl/B ratios indicate that the thermal fluids discharged by the intertidal vents and subaerial springs are similar, but they differ from those of submarine vents. Geoelectrical models depict an anomalous conductive trend from the La Jolla well to the Agua Caliente manifestation, suggesting the presence of a fault that allows upflow of hot water from depth. Lastly, integration of geochemical and geophysical data identified the best site for future exploration drilling at Punta Banda.     

薄层水平井地质导向技术在赵平3井的应用

赵平3井是布署在泌阳凹陷赵凹油田的一口水平井,设计水平段长152.07m,设计目的层厚度为2.6m,但从邻井资料分析,含油层段为1.8m厚,属薄层水平井。该井地质导向工作,钻前主要包括对资料的收集、分析、整理,重新处理邻井井斜资料,提前确定用来预测A靶点位置的对比标志层,并预测目的层深度、选择最佳靶心位置;钻进过程中主要包括进行地层对比分析,建立地质剖面,进行精细地层对比和着陆点分析。其中,水平段钻进地质导向以钻遇最大厚度油层为目标,同时兼顾工程实施的可行性。钻井施工中,确定一个合理的气体迟到时间、岩屑迟到时间以及准确识别真假新钻地层岩屑至关重要。水平段钻进过程中仍可能穿越顶底板及钻遇泥岩夹层,因此应不断进行井眼轨迹的调整,以保证钻进轨迹始终在油层中运行。水平井地质导向技术在赵平3井顺利实施。     

Analytical model of cold water front movement in a geothermal reservoir

Injection of cooled geothermal water back into the producing formation is a procedure that maintains reservoir pressure and increases energy extraction efficiency, but, because reinjected fluids tend to be much colder than the reservoir rock, injection can also cause cooling of the fluid produced from nearby wells. It is therefore essential to determine the cold front velocity in a geothermal reservoir. Constant thermal properties of both rock and fluid are generally assumed in order to solve this problem. In this paper, the rock density and heat capacity of the water–rock system as functions of temperature are assumed. Using the method of characteristics, an analytical solution is obtained. It is shown that the variable heat capacity of rock leads to a temperature-dependent speed of propagation of the thermal front. This results in a steepening of the front when cold water is injected into a hot zone, and eventually the formation of a discontinuous solution, or shock. A method is proposed for finding such discontinuous solutions and an equation for the velocity of the thermal front is presented. The difference between the front velocity obtained by means of the weak solution presented here and the classical model with constant thermal properties varies between about 1 and 14%.     

国内外抗高温钻井液降滤失剂研究与应用进展

综述了国内外近期钻井液降滤失剂的研究与进展,指出了抗高温降滤失剂的发展方向。就目前来看,国内虽然有部分产品性能已经达到了国际先进水平,但在超高温钻井液降滤失剂研究方面开展的工作较少,产业化速度慢,还不能满足超深井钻井的需要。今后在抗高温降滤失剂的研发方面。应做到环保、高效、低廉,并尽可能采用简单的生产工艺,以进一步降低产品的生产成本。     

国内钻井液及处理剂发展评述

国内开展钻井液研究与应用经历了起步、发展、完善和提高四个阶段。正是由于处理剂的发展,钻井液技术有了长足进步,钻井液由分散到不分散,到低固相、低或/和无黏土相钻井液发展过程中不断完善配套。不分散低固相聚合物钻井液、"三磺"钻井液、饱和盐水钻井液、聚磺钻井液、聚磺钾盐钻井液、两性离子聚合物钻井液、阳离子聚合物钻井液、正电胶钻井液、硅酸盐钻井液、氯化钙钻井液、有机盐钻井液、甲基葡萄糖苷钻井液、聚合醇钻井液、胺基抑制钻井液、超高温钻井液、超高密度钻井液等一系列钻井液体系,解决了不同时期、不同阶段、不同地区和不同复杂地质条件下的安全快速钻井难题。围绕井壁稳定、防漏堵漏机理和方法的研究成果的应用,有效减少了井下复杂的发生,保证了钻井质量。今后需要针对复杂地质条件下深井、超深井、大位移井钻井,以及页岩气水平井钻井的需要,从抗温、井壁稳定、润滑、防卡等方面,研究关键处理剂,实现处理剂系列化;减少关键处理剂在生产、流通及其他环节的浪费,提高产品质量;减少钻井液处理剂品种;在保证钻井液性能满足需要的前提下,尽可能降低钻井液处理剂用量;科学的选择和使用钻井液,重视油基钻井液的应用及技术水平的提高;并围绕绿色环保、抗高温抗盐的目标,开发高性能钻井液处理剂,建立钻井液及其处理剂的毒性检测评价手段,促进钻井液技术进步。     

The Bulalo geothermal field, Philippines: Reservoir characteristics and response to production

The Bulalo geothermal field has been operating since 1979, and currently has 330 MWe of installed capacity. The field is associated with a 0.5 Ma dacite dome on the southeastern flank of the Late Pliocene to Quaternary Mt. Makiling stratovolcano. The reservoir occurs within pre-Makiling andesite flows and pyroclastic rocks capped by the volcanic products of Mt. Makiling. Initially, the reservoir was liquid-dominated with a two-phase zone overlying the neutral-pH liquid. Exploitation has resulted in an enlargement of the two-phase zone, return to the reservoir of separated waste liquid that has been injected, scaling in the wellbores and rock formation, and influx of cooler groundwaters. Return of injected waters to the reservoir and scaling have been the major reservoir management concerns. These have been mitigated effectively by relocating injection wells farther away from the production area and by dissolving scale from wells with an acid treatment.