Analysis On Logging And Logging Interpretation Of Horizontal Wells In Chang 8 Reservoir Of Honghe Oilfield

The main production layer of Chang-8 reservoir of Yanchang Formation in Honghe oilfield is considered typical low permeability dense sandstone reservoir for the characteristics of fine grain sediment, thin-layer, various reservoir space types, complex pore structure, intense anisotropy, and uneven oil-bearing distribution. This kind of reservoir is developed mainly using large-scale horizontal well staged fracturing technology currently.Drilling data indicated that obvious interpretational inconformity for horizontal reservoir between well logging and mud logging, even difference somewhere, causes difficulty to make plan of layer selection for fracturing.This thesis is aimed to discuss key factors of difference between the well logging and mud logging from horizontal wells in Chang-8 reservoir of Honghe oilfield by contrast analysis for parameters of vertical well, diagonal well and horizontal well, and for well-mud logging interpretations of lithological distinguishing, ore-bearing grade, fracture zone prediction and average daily oil production of single well considering the regional geological setting. Main understandings are achieved as follows:1. The vertical and horizontal anisotropy of Chang-8 reservoir of Honghe oilfield is one of critical factors which cause difference of ore-bearing grade interpretations from well logging and mud logging for horizontal wells. The horizontal and vertical components of resistivity and other physical parameters differ greatly under the influence of geological anisotropy surrounding well. The surrounding dense wallrocks and/or well location in the reservoir can cause inconformity of well-mud logging parameters. The mud logging presents geological attributes in the well, while the well logging shows geological characteristics surrounding the well.2. Special drilling technology of horizontal well results in particularly fine cuttings returns to the wellhead. Complex well condition can increase cuttings’ residence time in the well. Oil and gas carried by cuttings losses more in horizontal well than in vertical well in consequence of fluorescence logging underrating and lithological distinguishing accuracy depression. Meanwhile, restricted by the gravity and well condition, cuttings be-detained on the lower wellface ("cuttings bed") can cause distortion of measured well logging parameters, such as shallow sounding interval transit time, micro electrode, gamma ray and density.3. The regional fracture system is developed generally, and is one of key factors which influence difference of well-mud logging interpretations and average daily oil production of single well. The horizontal well is easier to intersect the fracture zone than vertical well. The gravity influence for drilling three-dimensional hydrostatic pressure is absolutely different in horizontal wells and in vertical wells. Consequently, the strata release energy unusually and drilling fluid invades wall rocks unequally, which brings trouble for fracture recognition.4. Well logging and mud logging adopt different technology methods and analytical ways. The interference factors of each parameter are also different. Therefore, each evaluation has its limitation. It is meaningful to construct a comprehensive district-by-district and type-by-type evaluation system to improve the effect of well and mud logging data used in oilfield development plan-making, through combining the visibility of mud logging and high resolution of well logging, taking full account of the anisotropy and fracturing influence to the single well productivity, and quantitative classifying for horizontal section.