碳酸盐岩裂缝钻井漏失原因研究

A. Ruzhnikov
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引用次数: 3

摘要

裂缝性碳酸盐岩地层容易漏失,影响了井的施工过程,并对井的完整性产生长期影响。根据损失的性质(诱发性损失或与局部溶解有关的损失),当诱发性损失有很高的治愈机会时,成功率是不同的,而与溶解有关的损失可能需要很长时间,尽管多次尝试,成功率通常很低。为了更好地了解裂缝性碳酸盐岩的完全损失情况,开展了一系列研究。首先,为了了解漏失层的强度,通过环空液面和钻井液密度的影响对裂缝闭合压力进行了评估。其次,利用微电阻率图像、倾角数据和流体饱和多孔介质成像,研究了整个漏失循环带的地层性质。这些研究的结果带来了许多新的信息,并解释了一些以前的谜团。测量了漏失层的地层强度,并证实尽管井的其他施工参数发生了变化,地层强度仍然保持不变。此外,研究人员还证实,碳酸盐岩具有天然的高度裂缝性,沿井筒有900多条裂缝。对漏失循环带进行了表征,证实了漏失与裂缝无关,主要与岩溶、溶蚀和特大裂缝有关。确定了裂缝的大小和倾角,并证明了用常规材料处理裂缝的可能性。然而,在垂向真实深度下,已识别的巨型裂缝和岩溶带的尺寸超过裂缝的10倍,在水平井中,由于测量深度的原因,这种差异甚至更大。这一新信息有助于解释之前使用常规漏失材料的失败尝试。该手稿提供了新的信息,裂缝碳酸盐地层的表征,没有以前的文献。它可以根据漏失的性质调整地下和钻井视野,并进一步开发固化机制。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Study of the Cause of Lost Circulation while Drilling Fractured Carbonates
Fractured carbonate formations are prone to lost circulation, which affects the well construction process and has longtime effect on well integrity. Depending on the nature of losses (either induced or related to local dissolutions) the success rate is different when the induced losses can be cured with a high chance, and the one related to dissolutions may take a long time, and despite multiple attempts, the success rate is normally low. To have a better understanding of the complete losses across the fractured carbonates, a series of studies were initiated. First, to understand the strength of the loss zone, the fracture closing pressure was evaluated studying the fluid level in the annulus and back-calculating the effect of drilling fluid density. Second, the formation properties across the loss circulation zones were studied using microresistivity images, dip data, and imaging of fluid-saturated porous media. The results of the studies brought a lot of new information and explained some previous mysteries. The formation strength across the lost circulation zone was measured, and it was confirmed that it remains constant despite other changes of the well construction parameters. Additionally, it was confirmed that the carbonates are naturally highly fractured, having over 900 fractures along the wellbore. The loss circulation zone was characterized, and it was confirmed that the losses are not related to the fractures but rather to the karst, dissolution, and megafractures. The size and dip of the fractures were identified, and it was proven the possibility to treat them with conventional materials. However, the size of identified megafractures and karst zones exceeding the fractures by 10 times in true vertical depth, and in horizontal wells the difference is even higher due to measured depth. This new information helps to explain the previous unsuccessful attempts with the conventional lost circulation materials. The manuscript provides new information on the fractured carbonate formation characterization not available previously in the literature. It allows to align the subsurface and drilling visions regarding the nature of the losses and further develop the curing mechanisms.
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