巴西桑托斯盆地盐下漏失原因分析——以A井为例
Causes of Pre-Salt Losses in the Santos Basin, Brazil—Taking A Well as an Example

巴西桑托斯盆地盐下碳酸盐岩目的层中常发生井漏，但对于漏失原因认识还存在争议。本文以典型漏失的A井为例，基于录井、取芯、常规测井、成像测井等资料的综合分析，揭示了漏失层段储层控制因素及其形成机制。研究表明，A井盐下碳酸盐岩漏失主要发生在断裂或裂缝发育的层段，深部热液沿破碎带运移，对原生孔洞以及次生裂缝发生溶蚀、沉积，形成复杂的热液溶蚀储层，成为发生严重漏失的主要原因。桑托斯盆地盐下碳酸盐岩主要包括介壳灰岩、球粒灰岩、叠层石灰岩等多种类型，沉积时间仅13 Ma±、沉积物厚达数百米，不具备长期抬升暴露遭受淋滤形成典型喀斯特储层的必要条件。
Mud losses often occur in pre-salt carbonate layers in the Santos Basin of Brazil, but the under-standing of the controlling causes has not been clear. Taking the typical A well as an example, based on integrated analysis of muddy logging, coring, conventional logging and image logging, the reservoir controlling factors and mechanism for losses are revealed. The study shows that the losse of pre-salt carbonate layers in the A well mainly occurs in the intervals where faults or fractures are developed. Deep hydrothermal fluids migrate along the fracture zone, dissolving primary pores and secondary fractures and depositing, forming a complex hydrothermal dissolution reservoir which is responsible for the severe losses. The pre-salt carbonate sediments of Santos Basin mainly include coquinas, spherulites and stromatolites, et al. They form in a short geological time of 13 Ma± and the sedimentary thickness reaches several hundred meters, and do not have long-term uplift exposure and leaching, which are necessary conditions for typical karst development.