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New Developments in Sourceless Logging-While-Drilling Formation Evaluation:
A Case Study From Southern Italy
无化学源随钻测井地层评价新发展——意大利南部实例研究
Abstract
摘要
Radioactive chemical logging sources have been used in the E&P industry for many years to help operators obtain valuable information about their reservoirs. Until recently, much of the information obtained using these sources could not be obtained with any other method. While the potential risks involved with the use of such sources have always been known, more awareness in the industry has led to increased efforts towards the reduction or even elimination of the use of chemical sources where possible.
放射性化学测井源已经用于勘探及生产工业许多年，帮助作业者获取有用的储层信息。直到现在，许多信息的获取只能依靠放射源，别无它法。然而使用放射源潜在的危险众所周知，勘探生产作业者更是清楚，这就要求尽可能减少或者排除化学源的使用。
A new Logging-While-Drilling(LWD)tool has been developed, using innovative technology to provide a complete suite of formation evaluation measurements without having to use a chemical radioactive logging source. The use of a non-chemical radioactive source significantly reduces the environmental and operational risks normally involved with traditional LWD tools.
新研制的随钻测井仪，利用独特的技术，不使用放射性化学测井源而提供一套完整的地层评价测量结果。
The data delivered by this service include not only the traditional measurements such as gamma ray, resistivity, density, and neutron porosity, but also measurements not previously available in LWD such as formation capture cross section(sigma)and elemental analysis from neutron capture spectroscopy used to compute formation mineralogy. An entirely new LWD measurement has also been introduced with the tool, making it possible for the first time to determine formation density without the use of a chemical logging source.
这套服务设施提供的数据不仅包括伽马、电阻率、密度及中子孔隙度等传统测量结果，也包括以前仪器不能获得的，如地层的俘获截面和从中子俘获光谱中进行岩性分析，用于计算地层矿物成分。
A case study is presented of a well situated in a field in southern Italy, inside an environmentally sensitive national park. Because of the location of the well, it has not been possible to use radioactive logging sources for formation evaluation. As a result, fully evaluating the reserves has been an ongoing challenge for the operator. In addition, because of the move towards high angle and horizontal wells, wireline
formation evaluation acquisition has been, at times, replaced by LWD.
实例是意大利南部的一个井场，位于一个对环境特别敏感的国家公园内。由于井场的位置，不可能使用放射性测井源来进行地层评价。结果详细评价储层就成为作业者随后的挑战。另外，由于大角度井和水平井的发展，电缆地层评价获取地层信息有时被随钻测井所取代。
The new LWD tool allowed the operator to not only improve efficiency, but also brought with it the possibility of more completely evaluating the diagenetically complex tight carbonate reservoir through the use of the new measurements. The favourable environmental conditions (low temperature and low mud salinity) made it possible to obtain additional spectral data, which was used to correct the neutron porosity measurement for lithology effects, despite the presence of dolomite.
新的随钻测井仪不仅能提高效率，而且通过新的测量结果能对极其复杂坚硬的碳酸盐岩层进行完整的评价。在低温和低的泥浆矿化度等有利环境条件下，可以获得额外的光谱数据，用于校正岩性影响的中子孔隙度测量结果，尽管现场描述为白云岩。
The results of the formation evaluation studies are presented, together with an analysis of the impact on operational efficiency and environmental and operational safety as a result of not having to use a chemical logging source.
作为不使用化学测井源的结果，地层评价的研究结果包括对操作效率的影响、环境影响和操作安全性影响的分析。
Introduction and Geological Setting
简介和地质环境
Understanding the porosity distribution and type within a reservoir is the first step in order to accurately quantify reserves and design proper field development scenarios.
Porosity heterogeneities within complex carbonate sequences can cause the potential of a reservoir to be inaccurately evaluated when only conventional approaches, such as density, neutron and sonic logs, are used. Image logs and surface logging data have been recognized as being essential for correct petrophysical characterization of these reservoirs.
了解储集层中的孔隙分布和类型是首要步骤，以便准确定量分析储层和设计正确的油田开发方案。在复杂的碳酸盐岩层序中孔隙各向异性分布，仅用传统的测井方法如：密度、中子和声波测井等评价为潜在油藏，这是不准确的评估结果。成像测井和表面测井数据经过验证作为校正这些储藏的石油物理特性的重要依据。
The Val d’Agri carbonate reservoir of the Inner Apulian platform in the south of Italy is difficult to evaluate due to its complex porous system and structural framework.The field is a heterogeneous geological structure where diagenetic processes,mainly dolomitization and significantly affect the reservoir properties. Furthermore, the degree of dolomitization and the complex tectonic evolution of the area have had a significant influence on fracture development and distribution within the carbonate strata. Diagenesis, which occurred during early stage of the sedimentation, has both increased and/or decreased reservoir quality. In places, dolomitization and leaching have enhanced the reservoir porosity and permeability. Dolomitization is especially in the Albian–Cenomanian depositional sequences. Dolomized lithotypes present secondary porosity, often vacuolar and in some cases biomoldic, where bioclasts have been completely removed by dissolution. The karst process, recognizable in unconformity surfaces and subaerial exposure surfaces, produced a complex system of caves and contribute in opening by dissolution some of the tectonic fractures.
意大利南部阿普利亚内部Val d’Agri区的碳酸盐岩储集层由于其复杂的多孔体系和结构框架很难进行地层评价。这一区域是各向异性的地质构造，变质过程主要是白云石化和喀斯特化，对储层的性质产生了及其深远的影响。而且，这一地区白云石化的程度和复杂的构造演化对碳酸盐岩地层裂缝发育和分布产生重要的影响。变质作用发生在沉积作用的前期，既能提高也能降低储层的质量。在某些地区，白云石化和渗透作用提高了储层的孔隙度和渗透率。白云石化在阿尔必阶—森诺曼阶沉积层序中表现的尤为明显。白云质岩性类型表现为次生孔隙度，多空泡有时会有生物痕迹，这是因为生物碎屑岩已经完全被溶解掉了。喀斯特地貌可以在不均质地表面和地下暴露地表部分识别，产生一个复杂的溶洞体系，通过溶解有助于形成一些构造裂缝。
In other places, diagenesis has seriously decreased the porosity and permeability. The reservoir properties of the karst system were subsequently reduced by sediment infilling and mineral precipitation under vadose conditions and, above all, during the burial compaction.
在其他地区，变质作用严重降低地层孔隙度和渗透率。喀斯特体系的储层孔隙在渗流条件下，压实过程中，被沉淀物和矿物质迅速充填。
Therefore, reservoir properties are extremely variable depending on the amount of the various different diagenetic effects. In a low porosity background, there are some patches with better hydraulic potential. The fracture network is characterized by medium and high angle events, locally associated to cataclastic zones.
因此，储层的特性随着不同的变质效果而相应变化。在低孔隙度的地方，具有较好的水力势能点。裂缝以中高角度为特征，局部与碎裂层有关。
Operational Constraints
操作限制
In addition to the above heterogeneous scenario, the Val d’Agri field development presents some operational constraints due to the restrictive local environmental
regulations, which are a result of the area having been formally declared as a National Park. Because of the environmental regulations, it is not possible to use radioactive
logging sources for formation evaluation. In addition, because of the high angle and horizontal trajectories, log data acquisition in the past has not been very successful. Pipe-conveyed logging strings(TLC)have often hung up in the 8-1/2 in. section, which can have deviations up to 80 degrees, high dogleg severities, and difficult borehole conditions. Furthermore, the presence of residual argillite and/or vulcanite layers may create significant washouts. Up to now the percentage of successful logging in the extended 6 in. reservoir drains, sometimes up to 3000 m long,has been very limited. As a result, reserves evaluation has been an ongoing challenging task for the operator.
除了上述的各向异性外，Val d’Agri地区已正式宣布为国家公园，由于当地环境法规的限制，油田开发提出了一些操作限制。由于环境法规的限制，不可能使用放射性测井源进行地层评价。另外，由于大角度井和水平井中，过去的测井数据获取不是很成功。管路传输测井数据串一般用于8.5英寸井眼、当井斜高达80度、高狗腿度和井况差的情况无法使用。而且，残余硅质粘土岩和硬橡皮地层的存在，可能出现很深的冲洗带。直到现在，在6英寸井眼、排干的油藏，长达3000米的井眼的成功几率大大降低。这样，储层评价就成为作业者面临的主要挑战。
Many of these challenges have been addressed by using a Logging While Drilling(LWD)system as the formation evaluation acquisition method. A laterolog azimuthal resistivity tool, geoVISION*, allowed for high-resolution resistivity image acquisition, while porosity and lithology measurements were obtained with a non-chemical radioactive source device, the EcoScope*tool. The EcoScope
helped to reduce the environmental and operational risks that would normally be associated with traditional LWD tools.
许多挑战通过使用随钻测井体系作为地层评价获取手段已经得到解决。双侧向方位电阻率测井仪geoVISION*获得高分辨率电阻率成像资料，而孔隙度和岩性的测量是通过一个不含化学放射性源的装置—EcoScope*。EcoScope*与传统随钻测井仪相比，能够减小环境污染并降低操作者的风险。
The LWD string was run in wash-down mode and in reaming conditions on a sidetrack of an existing well in the Val d’Agri field. The program was designed to achieve a complete assessment and validation of reservoir porosity. The high formation resistivities, up to 200,000 ohm-m, made the geoVISION the only possible choice to evaluate the Val d’Agri carbonates. Conventional LWD propagation measurements are not accurate enough in this environment.
在Val d’Agri油田已经存在的井中，随钻测井仪器串采用边下边洗的模式，在扩眼的条件下使用侧钻。设计程序获得完整的地层评估和有效的储集层孔隙度。地层电阻率高达200000 ohm-m，使geoVISION成为Val d’Agri地区碳酸盐岩评估的唯一选择。传统的随钻测井测量结果在这种环境中不够准确。
The LWD data were also compared to core data and to a set of wireline logs, including the Fullbore Formation MicroImager(FMI*)and Accelerator Porosity Sonde(APS*) tools.
这种随钻测井的数据也和岩心数据和电缆测井数据做对比，包括全井眼地层微电阻率成像和加速型孔隙度探测器。
LWD Tools and Technique
随钻测井仪及其技术
The geoVISION imaging resistivity tool is a laterolog resistivity device. An integral, cylindrical electrode provides a high-resolution, lateral resistivity measurement called ring resistivity. In addition to the ring resistivity, a button sleeve with three focused electrodes provides detailed azimuthal resistivity measurements with different depths of investigation. These azimuthally acquired button measurements are displayed as fullbore images to describe formation resistivity contrasts.Although the resolution of the images is not as high as some wireline imaging tools such as the FMI, the tool still provides detailed geological images of bedding and fractures.
geoVISION成像电阻率仪器是一个侧向电阻率设备。一个完整的圆柱形电极提供高分辨率侧向电阻率测量结果，称环形电阻率。另外，环形电阻率一个按钮套筒带有三个聚焦电极，提供详细的不同探测深度的方位电阻率测量结果。这些方位测量结果以全井眼成像的形式展现，进行地层电阻率对比。虽然该成像的分辨率低于电缆成像测井仪如FMI，但是仪器仍然能够提供详细的地质层位和裂缝成像。
The porosity and lithology measurements were acquired by the new multifunctional LWD tool, EcoScope. The EcoScope uses innovative technology to provide a complete suite of both drilling and formation evaluation measurements, in a single collar, without having to use a chemical radioactive logging source.
孔隙度和岩性测量可以通过这种新的多功能LWD测井仪—EcoScope获得。EcoScope采用一种新颖的技术提供一套完整的钻井和地层评价测量结果，在一个单独的钻铤内，不使用化学放射性测井源。
The data delivered by this service include not only the traditional measurements such as annular pressure while drilling(APWD*),calipers, gamma ray, propagation resistivity, bulk density, and porosity, but also measurements not previously available in LWD such as formation capture cross section and elemental analysis from neutron capture spectroscopy used to compute formation mineralogy. An entirely new LWD measurement, described below, has also been introduced with the tool. This makes it possible for the first time to determine formation bulk density without the use of a chemical logging source.
这种仪器传递的数据不仅包括传统的测量结果，像随钻环空压力、井径、伽马、电阻率、岩性密度和孔隙度，也包括以前随钻测井得不到的，例如，地层俘获截面和从中子俘获光谱中进行元素分析，用来计算地层矿物含量。一个崭新的测量结果，描述见下，也被这种仪器获得。这使第一次不使用化学测井源确定岩性密度成为可能。
The tool has a pulsed neutron generator(PNG)that allows neutrons to be generated only when the tool is powered, eliminating the need for an americium beryllium(Am-Be) chemical neutron source. The PNG also enables several new
LWD measurements, such as: Best-Phi*porosity, a hydrogen index equivalent; elemental capture spectroscopy; formation capture cross section(sigma),which can act as an alternative to resistivity measurements for fluid saturation calculations; and Neutron Gamma Density(NGD*),which is a density measurement obtained from the gamma rays generated from neutron interactions with the formation.
这种测井仪有一个脉冲中子发生器，仅当仪器供电时产生中子，这就排除了使用镅铍化学中子源。脉冲中子发生器也能提供几个新的LWD的测量结果，如：最佳孔隙度、含氢指数当量、元素俘获光谱、地层俘获截面。俘获截面可以充当电阻率测量的替代物用于流体饱和度计算。中子密度是从中子与地层的相互作用产生的伽马射线上获取的。
