川东宣汉—开江地区恶性井漏特征及地质因素

CHARACTERISTICS AND GEOLOGICAL FACTORS OF VICIOUS LOST CIRCULATION IN XUANHAN—KAIJIANG AREA OF EAST SICHUAN

川东北部宣汉—开江地区目前为川东地区天然气勘探的主要区块,钻井中井漏普遍,给钻井生产带来重大损失,严重影响井下施工安全。因此,正确认识漏失的性质、原因以预防和采取有效措施治理井漏是宣汉—开江地区钻井中迫切需要解决的问题。文章对宣汉—开江地区恶性井漏的特点及地质因素进行了分析,该区恶性井漏的特点是漏失井段长,漏失层段多,漏速大,漏失量大;沙溪庙组—自流井组、嘉五1 亚段及飞仙关组地层恶性井漏特征明显,发生的频率高。资料表明,发生恶性井漏的漏层的漏失通道及储液空间主要为大型溶洞或大型裂缝系统;纵向压力剖面上,近地表正常静水柱压力带常发生恶性井漏,压力过渡带恶性井漏发生的频率相对较高,异常高压带较少发生恶性井漏;不同的压力带及复杂压力系统共存条件下,容易产生新的漏失通道或储液空间,诱发恶性漏失。

The Xuanhan - Kaijiang area of Northeast Sichuan is the major region currently for gas exploration. Lost circulation is a common problem in the area, which brings big loss for drilling and affects safety for down-hole operation. Therefore, it is the problem to solve urgently for drilling in Xuanhan - Kaijiang area to correctly understand the property and reasons of lost circulation, prevent and take effective measures for controlling lost circulation. The article analyzes the characteristics and geological factors of the vicious lost circulation in Xuanhan - Kaijiang area. The characteristics of the vicious lost circulation in the area are: the hole interval of lost circulation is long; the layers of lost circulation are lot; the rate of lost circulation is high and the volume of lost circulation is large. The vicious lost circulation appears obviously and happens frequently in the formations of Shaximiao group-ziliujing group; Jiawu sub-section and Feixianguan group. The data show the loss channels and the liquid-storing spaces mainly are big caves and large fracture system for the formations where the vicious lost circulation happens. On the vertical pressure profile, the vicious lost circulation happens often in the normal static water pressure belt near the surface. The frequency the vicious lost circulation happens at is relatively high in the pressure transitional zones. The vicious lost circulation happens less in the abnormal high-pressure zones. It is easy to produce the new loss channels and liquid-storing spaces and induce the vicious lost circulation when the different pressure zones and complicated pressure system exist simultaneously.